diff --git a/lib/customerio/client.rb b/lib/customerio/client.rb
index ffb8754..61cf8a9 100644
--- a/lib/customerio/client.rb
+++ b/lib/customerio/client.rb
@@ -44,6 +44,14 @@ def unsuppress(customer_id)
       @client.request_and_verify_response(:post, unsuppress_path(customer_id))
     end
 
+    def unique_track(event_id, customer_id, event_name, attributes = {})
+      raise ParamError.new("event_id must be a valid ULID") if !valid_ulid?(event_id)
+      raise ParamError.new("customer_id must be a non-empty string") if is_empty?(customer_id)
+      raise ParamError.new("event_name must be a non-empty string") if is_empty?(event_name)
+  
+      create_customer_event(customer_id, event_name, attributes, event_id)
+    end
+
     def track(customer_id, event_name, attributes = {})
       raise ParamError.new("customer_id must be a non-empty string") if is_empty?(customer_id)
       raise ParamError.new("event_name must be a non-empty string") if is_empty?(event_name)
@@ -157,10 +165,11 @@ def create_or_update(attributes = {})
       @client.request_and_verify_response(:put, url, attributes)
     end
 
-    def create_customer_event(customer_id, event_name, attributes = {})
+    def create_customer_event(customer_id, event_name, attributes = {}, event_id = nil)
       create_event(
         url: "#{customer_path(customer_id)}/events",
         event_name: event_name,
+        event_id: event_id,
         attributes: attributes
       )
     end
@@ -183,11 +192,12 @@ def create_pageview_event(customer_id, page, attributes = {})
       )
     end
 
-    def create_event(url:, event_name:, anonymous_id: nil, event_type: nil, attributes: {})
+    def create_event(url:, event_name:, anonymous_id: nil, event_type: nil, event_id: nil, attributes: {})
       body = { :name => event_name, :data => attributes }
       body[:timestamp] = attributes[:timestamp] if valid_timestamp?(attributes[:timestamp])
       body[:anonymous_id] = anonymous_id unless is_empty?(anonymous_id)
       body[:type] = event_type unless is_empty?(event_type)
+      body[:id] = event_id unless is_empty?(event_id)
 
       @client.request_and_verify_response(:post, url, body)
     end
@@ -196,6 +206,10 @@ def valid_timestamp?(timestamp)
       timestamp && timestamp.is_a?(Integer) && timestamp > 999999999 && timestamp < 100000000000
     end
 
+    def valid_ulid?(ulid)
+      !!(ulid =~ /\A[0123456789ABCDEFGHJKMNPQRSTVWXYZabcdefghjkmnpqrstvwxyz]{26}\z/)
+    end
+
     def is_empty?(val)
       val.nil? || (val.is_a?(String) && val.strip == "")
     end
diff --git a/spec/client_spec.rb b/spec/client_spec.rb
index dfd9321..f42815e 100644
--- a/spec/client_spec.rb
+++ b/spec/client_spec.rb
@@ -392,6 +392,25 @@ def json(data)
       client.track(5, "purchase", type: "socks", price: "13.99", timestamp: "Hello world")
     end
 
+    context "tracking a unique event" do
+      let(:event_id) { "01HB4HBDKTFWYZCK01DMRSWRFD" }
+
+      it "throws an error when event_id is invalid ulid" do
+        stub_request(:put, /track.customer.io/)
+          .to_return(status: 200, body: "", headers: {})
+
+        lambda { client.unique_track(" ", 1, "test_event") }.should raise_error(Customerio::Client::ParamError, "event_id must be a valid ULID")
+      end
+
+      it "sends a POST request to the customer.io's anonymous event API" do
+        stub_request(:post, api_uri("/api/v1/customers/5/events/#{event_id}")).
+          with(body: { name: "purchase", data: {} }).
+          to_return(status: 200, body: "", headers: {})
+
+        client.unique_track(event_id, 5, "purchase")
+      end
+    end
+
     context "tracking an anonymous event" do
       let(:anon_id) { "anon-id" }