diff --git a/services/identity/src/client_service.rs b/services/identity/src/client_service.rs
--- a/services/identity/src/client_service.rs
+++ b/services/identity/src/client_service.rs
@@ -42,10 +42,10 @@
   is_valid_ethereum_address, parse_and_verify_siwe_message, SocialProof,
 };
 use crate::token::{AccessTokenData, AuthType};
-
 pub use crate::grpc_services::protos::unauth::identity_client_service_server::{
     IdentityClientService, IdentityClientServiceServer,
   };
+use crate::regex::is_valid_username;
 
 #[derive(Clone, Serialize, Deserialize)]
 pub enum WorkflowInProgress {
@@ -102,6 +102,12 @@
     let message = request.into_inner();
     debug!("Received registration request for: {}", message.username);
 
+    if !is_valid_username(&message.username)
+      || is_valid_ethereum_address(&message.username)
+    {
+      return Err(tonic::Status::invalid_argument("invalid username"));
+    }
+
     self.check_username_taken(&message.username).await?;
     let username_in_reserved_usernames_table = self
       .client
@@ -113,9 +119,7 @@
       return Err(tonic::Status::already_exists("username already exists"));
     }
 
-    if RESERVED_USERNAME_SET.contains(&message.username)
-      || is_valid_ethereum_address(&message.username)
-    {
+    if RESERVED_USERNAME_SET.contains(&message.username) {
       return Err(tonic::Status::invalid_argument("username reserved"));
     }
 
diff --git a/services/identity/src/constants.rs b/services/identity/src/constants.rs
--- a/services/identity/src/constants.rs
+++ b/services/identity/src/constants.rs
@@ -228,3 +228,8 @@
   ];
   pub const ALLOW_ORIGIN_LIST: &str = "ALLOW_ORIGIN_LIST";
 }
+
+// Regex
+
+pub const VALID_USERNAME_REGEX_STRING: &str =
+  r"^[a-zA-Z0-9][a-zA-Z0-9-_]{0,190}$";
diff --git a/services/identity/src/main.rs b/services/identity/src/main.rs
--- a/services/identity/src/main.rs
+++ b/services/identity/src/main.rs
@@ -16,6 +16,7 @@
 mod id;
 mod keygen;
 mod nonce;
+mod regex;
 mod reserved_users;
 mod siwe;
 mod sync_identity_search;
diff --git a/services/identity/src/regex.rs b/services/identity/src/regex.rs
new file mode 100644
--- /dev/null
+++ b/services/identity/src/regex.rs
@@ -0,0 +1,54 @@
+use regex::Regex;
+
+use crate::constants::VALID_USERNAME_REGEX_STRING;
+
+pub fn is_valid_username(candidate: &str) -> bool {
+  let valid_username_regex = Regex::new(VALID_USERNAME_REGEX_STRING)
+    .expect("regex pattern should be valid");
+  valid_username_regex.is_match(candidate)
+}
+
+#[cfg(test)]
+mod tests {
+  use super::*;
+
+  #[test]
+  fn test_valid_username_with_dash_and_underscore() {
+    assert!(is_valid_username("WRx16rC_VWX-"),);
+  }
+
+  #[test]
+  fn test_valid_username_with_minimum_length() {
+    assert!(is_valid_username("a"));
+  }
+
+  #[test]
+  fn test_valid_username_with_maximum_length() {
+    assert!(is_valid_username(
+      "Dg75raz1KL0rzqFbnUDAtSp0KfvDThPGcYGHiEin9m7LCWYJ7vQYNkXpbTNJ7MYaaTeqApgYDr3XdNX0BmKetP0iJeKRZuDdSEuybnGrdivwSQPLrJ8rv2WMTGvNjjDypvMMbDXmQ7wt0jPFfKD41Uc07SkPFcBJkwBJ8WJuJWmm7m0nvxhFRieQn319qHk"
+    ));
+  }
+
+  #[test]
+  fn test_invalid_username_too_short() {
+    assert_eq!(is_valid_username(""), false);
+  }
+
+  #[test]
+  fn test_invalid_username_too_long() {
+    assert_eq!(
+      is_valid_username("XVnYhmjPrVpSwLZnSGjdnx5mmRFLbSh5RjjqU7Wf62LXe9Hyy0CfJQNXgTy62Uxzip538MMYtwvaqqA0fukYijWAuZdVVpYRMuaZ0gzxLgV6hzF9amvnjZGYgdKeEX45WErYq2nN7Q2ivcFfftWnpudPcPr0pxWRLdmqS37jNVHWMX919vXz0PdzeLNHx0TW"),
+      false
+    );
+  }
+
+  #[test]
+  fn test_invalid_username_first_char_non_alphanumeric() {
+    assert_eq!(is_valid_username("-asdf"), false);
+  }
+
+  #[test]
+  fn test_invalid_username_invalid_symbol() {
+    assert_eq!(is_valid_username("asdf$"), false);
+  }
+}