This prospective study assessed the sexual and psychosocial effects of 12 months' use of an external vacuum device in the treatment of erectile dysfunction. Results showed that the external vacuum device produced erections sufficient for intercourse in 87% of the men in our sample. The dropout rate was only 20% over the 12-month period. Use of the external vacuum device was associated with improvements in men's and their partners' sexual functioning. These improvements included erections of better quality, increased partner arousal, and increased frequency of orgasm and sexual satisfaction for men and women. The external vacuum device was also associated with decreases in general psychiatric symptomatology for men. Similar improvements in psychological functioning were not found for partners. Side effects and factors in patient and partner acceptance of the external vacuum device are discussed.