Exhibit 21

|Subsidiaries                                           |                                                                                 | State or Country
of Incorporation
|------------------------------------------------------ | ------------------------------------------------------------------------------- | ---------------------------------
|All subsidiaries are wholly owned except as indicated. |                                                                                 |                                  
|Bally Technologies, Inc.                               |                                                                                 | Nevada                           
|Alliance Holding Company                               |                                                                                 | Nevada                           
|                                                       | Bally Gaming International, Inc.                                                |                                  
|                                                       |                                                                                 | Bally Gaming, Inc.               
|                                                       |                                                                                 |                                  
|                                                       |                                                                                 |                                  
|                                                       |                                                                                 |                                  
|                                                       |                                                                                 |                                  
|                                                       |                                                                                 |                                  
|                                                       |                                                                                 |                                  
|                                                       |                                                                                 |                                  
|                                                       |                                                                                 |                                  
|                                                       |                                                                                 |                                  
|                                                       |                                                                                 |                                  
|                                                       |                                                                                 |                                  
|                                                       |                                                                                 |                                  
|                                                       |                                                                                 |                                  
|                                                       |                                                                                 |                                  
|                                                       |                                                                                 |                                  
|                                                       |                                                                                 |                                  
|                                                       |                                                                                 |                                  
|                                                       |                                                                                 |                                  
|Casino Electronics, Inc.                               |                                                                                 | Nevada                           
|Foreign Gaming Ventures, Inc.                          |                                                                                 | Nevada                           
|                                                       | United Gaming Rainbow                                                           |                                  
|                                                       | Rainbow CasinoVicksburg Partnership, L.P. (a Mississippi limited partnership)* |                                  

---

---



QuickLinks