diff --git a/README.md b/README.md
index 05692ff..2eed0f9 100644
--- a/README.md
+++ b/README.md
@@ -126,6 +126,11 @@ Returns the total number of data in the quadtree.
 
 Returns the datum closest to the position ⟨*x*,*y*⟩ with the given search *radius*. If *radius* is not specified, it defaults to infinity. If there is no datum within the search area, returns undefined.
 
+<a name="quadtree_findInCircle" href="#quadtree_findInCircle">#</a> <i>quadtree</i>.<b>findInCircle</b>(<i>x</i>, <i>y</i>[, <i>radius</i>][, <i>filter</i>])
+ [<>](https://github.com/d3/d3-quadtree/blob/master/src/findInCircle.js "Source")
+
+Returns all the data within the given search *radius* of the position ⟨*x*,*y*⟩ that satisfy the filter *filter*, if specified. If *radius* is not specified, it defaults to infinity. If there is no acceptable datum within the search area, returns an empty array.
+
 <a name="quadtree_visit" href="#quadtree_visit">#</a> <i>quadtree</i>.<b>visit</b>(<i>callback</i>)
  [<>](https://github.com/d3/d3-quadtree/blob/master/src/visit.js "Source")
 
diff --git a/src/findInCircle.js b/src/findInCircle.js
new file mode 100644
index 0000000..1ad3a10
--- /dev/null
+++ b/src/findInCircle.js
@@ -0,0 +1,22 @@
+export default function(x, y, radius, filter) {
+  const quadtree = this,
+    result = [],
+    radius2 = radius * radius,
+    accept = filter
+      ? d => filter(d) && result.push(d)
+      : d => result.push(d);
+
+  quadtree.visit(function(node, x1, y1, x2, y2) {
+    if (node.length) {
+      return x1 >= x + radius || y1 >= y + radius || x2 < x - radius || y2 < y - radius;
+    }
+
+    const dx = +quadtree._x.call(null, node.data) - x,
+          dy = +quadtree._y.call(null, node.data) - y;
+    if (dx * dx + dy * dy < radius2) {
+      do { accept(node.data); } while (node = node.next);
+    }
+  });
+  
+  return result;
+}
diff --git a/src/quadtree.js b/src/quadtree.js
index 5d58593..2bad3d4 100644
--- a/src/quadtree.js
+++ b/src/quadtree.js
@@ -3,6 +3,7 @@ import tree_cover from "./cover.js";
 import tree_data from "./data.js";
 import tree_extent from "./extent.js";
 import tree_find from "./find.js";
+import tree_findInCircle from "./findInCircle.js";
 import tree_remove, {removeAll as tree_removeAll} from "./remove.js";
 import tree_root from "./root.js";
 import tree_size from "./size.js";
@@ -63,6 +64,7 @@ treeProto.cover = tree_cover;
 treeProto.data = tree_data;
 treeProto.extent = tree_extent;
 treeProto.find = tree_find;
+treeProto.findInCircle = tree_findInCircle;
 treeProto.remove = tree_remove;
 treeProto.removeAll = tree_removeAll;
 treeProto.root = tree_root;
diff --git a/test/findInCircle-test.js b/test/findInCircle-test.js
new file mode 100644
index 0000000..c0ea45a
--- /dev/null
+++ b/test/findInCircle-test.js
@@ -0,0 +1,21 @@
+var tape = require("tape"),
+    d3_quadtree = require("../");
+
+tape("quadtree.findInCircle(x, y, radius) returns all the points within the search radius of the given [x, y]", function(test) {
+  const points = [[0, 0], [100, 0], [0, 100], [100, 100]];
+  const q = d3_quadtree.quadtree(points);
+  test.deepEqual(q.findInCircle(20, 20, Infinity), points);
+  test.deepEqual(q.findInCircle(20, 20, 20 * Math.SQRT2 + 1e-6), [points[0]]);
+  test.deepEqual(q.findInCircle(20, 20, 20 * Math.SQRT2 - 1e-6), []);
+  test.deepEqual(q.findInCircle(50, 0, 51), [points[0], points[1]]);
+  test.end();
+});
+
+tape("quadtree.findInCircle(x, y, radius, filter) returns all the points within the search radius of the given [x, y] and passing filter", function(test) {
+  const points = [[0, 0, "a"], [0, 0, "b"], [100, 0, "a"], [0, 100, "b"], [100, 100, "a"]];
+  const q = d3_quadtree.quadtree(points);
+  const filter = d => d[2] === "a";
+  test.deepEqual(q.findInCircle(20, 20, Infinity, filter), points.filter(filter));
+  test.deepEqual(q.findInCircle(0, 0, 2, filter), [points[0]]);
+  test.end();
+});