I have a module which creates records in the db via drupal_write_record and this works perfectly. However I need to get the automatically assigned serial number for each record which is written into a variable.

Does anyone know how I can achieve this and get the index #?

I need the index variable to use in another table to create the reference...

Edit: Clives answer worked as below:

// Create object
$call = new stdClass;  
$call->uid = $user->uid;
$call->call_type = $call_type;
$call->cli = $cli;
$call->start_nid = NULL;
$call->timestamp = $timestamp;
    
// Insert call row in db  
drupal_write_record($table,$call);

// Test correct index
drupal_set_message($call->call_id);