| 1991 Thriftway ATP Championships | |
|---|---|
| Date | August 5–11 |
| Edition | 90th |
| Draw | 56S / 28D |
| Prize money | $1,020,000 |
| Surface | Hard / outdoor |
| Location | Mason, Ohio, U.S. |
| Venue | Lindner Family Tennis Center |
| Champions | |
| Singles | |
 Guy Forget[1] | |
| Doubles | |
 Ken Flach / Robert Seguso[2] | |
The 1991 Cincinnati Open, known by the corporate title of the Thriftway ATP Championships was a tennis tournament played on outdoor clay courts. It was the 90th edition of the tournament and was part of the ATP Super 9 of the 1991 ATP Tour It took place in Mason, Ohio, United States, from August 5 through August 11, 1991.
The tournament had previously appeared on the Tier III of the WTA Tour but no event was held from 1989 to 2003.
