diff --git a/doc/release-notes.md b/doc/release-notes.md
--- a/doc/release-notes.md
+++ b/doc/release-notes.md
@@ -4,4 +4,5 @@
 
 This release includes the following features and fixes:
  - Add `signrawtransactionwithkey` and `signrawtransactionwithwallet` RPCs.
-   These are specialized subsets of the `signrawtransaction` RPC.
\ No newline at end of file
+   These are specialized subsets of the `signrawtransaction` RPC.
+ - Deprecate `nblocks` parameter in `estimatefee`.  See `bitcoin-cli help estimatefee` for more info. Use `-deprecatedrpc=estimatefee` to temporarily re-enable the old behavior while you migrate.
diff --git a/src/rpc/mining.cpp b/src/rpc/mining.cpp
--- a/src/rpc/mining.cpp
+++ b/src/rpc/mining.cpp
@@ -774,36 +774,29 @@
 
 static UniValue estimatefee(const Config &config,
                             const JSONRPCRequest &request) {
-    if (request.fHelp || request.params.size() != 1) {
+    if (request.fHelp || request.params.size() > 1) {
         throw std::runtime_error(
-            "estimatefee nblocks\n"
+            "estimatefee\n"
             "\nEstimates the approximate fee per kilobyte needed for a "
-            "transaction to begin\n"
-            "confirmation within nblocks blocks.\n"
-            "\nArguments:\n"
-            "1. nblocks     (numeric, required)\n"
+            "transaction\n"
             "\nResult:\n"
             "n              (numeric) estimated fee-per-kilobyte\n"
-            "\n"
-            "A negative value is returned if not enough transactions and "
-            "blocks\n"
-            "have been observed to make an estimate.\n"
-            "-1 is always returned for nblocks == 1 as it is impossible to "
-            "calculate\n"
-            "a fee that is high enough to get reliably included in the next "
-            "block.\n"
             "\nExample:\n" +
-            HelpExampleCli("estimatefee", "6"));
+            HelpExampleCli("estimatefee", ""));
     }
 
-    RPCTypeCheck(request.params, {UniValue::VNUM});
-
-    CFeeRate feeRate = g_mempool.estimateFee();
-    if (feeRate == CFeeRate(Amount::zero())) {
-        return -1.0;
+    if ((request.params.size() == 1) &&
+        !IsDeprecatedRPCEnabled(gArgs, "estimatefee")) {
+        // FIXME: Remove this message in 0.20
+        throw JSONRPCError(
+            RPC_METHOD_DEPRECATED,
+            "estimatefee with the nblocks argument is no longer supported\n"
+            "Please call estimatefee with no arguments instead.\n"
+            "\nExample:\n" +
+                HelpExampleCli("estimatefee", ""));
     }
 
-    return ValueFromAmount(feeRate.GetFeePerK());
+    return ValueFromAmount(g_mempool.estimateFee().GetFeePerK());
 }
 
 // clang-format off
diff --git a/test/functional/rpc_estimatefee.py b/test/functional/rpc_estimatefee.py
--- a/test/functional/rpc_estimatefee.py
+++ b/test/functional/rpc_estimatefee.py
@@ -6,27 +6,40 @@
 from decimal import Decimal
 
 from test_framework.test_framework import BitcoinTestFramework
-from test_framework.util import assert_equal
+from test_framework.util import assert_equal, assert_raises_rpc_error
 
 
 class EstimateFeeTest(BitcoinTestFramework):
     def set_test_params(self):
         self.setup_clean_chain = True
-        self.num_nodes = 2
-        self.extra_args = [[], ["-minrelaytxfee=0.001"]]
+        self.num_nodes = 3
+        self.extra_args = [[], ["-minrelaytxfee=0.001"],
+                           ["-deprecatedrpc=estimatefee"]]
 
     def run_test(self):
+        default_node = self.nodes[0]
+        diff_relay_fee_node = self.nodes[1]
+        deprecated_node = self.nodes[2]
         for i in range(5):
             self.nodes[0].generate(1)
 
             # estimatefee is 0.00001 by default, regardless of block contents
-            assert_equal(self.nodes[0].estimatefee(i), Decimal('0.00001'))
-            # Also test named arguments
-            assert_equal(self.nodes[0].estimatefee(
-                nblocks=i), Decimal('0.00001'))
+            assert_equal(default_node.estimatefee(), Decimal('0.00001'))
+            assert_equal(deprecated_node.estimatefee(), Decimal('0.00001'))
 
             # estimatefee may be different for nodes that set it in their config
-            assert_equal(self.nodes[1].estimatefee(i), Decimal('0.001'))
+            assert_equal(diff_relay_fee_node.estimatefee(), Decimal('0.001'))
+
+        # nblocks arg is no longer supported. Make sure the error message
+        # indicates this.
+        assert_raises_rpc_error(-32, "estimatefee with the nblocks argument is no longer supported",
+                                default_node.estimatefee, 1)
+
+        # When marked as deprecated, estimatfee with nblocks set succeeds
+        assert_equal(deprecated_node.estimatefee(1), Decimal('0.00001'))
+        # Also test named arguments
+        assert_equal(deprecated_node.estimatefee(
+            nblocks=1), Decimal('0.00001'))
 
 
 if __name__ == '__main__':