Serotonin reuptake inhibitor (SRI) antidepressants have been associated with sexual dysfunction, though there have been few prospective reports specifically examining this problem. The purpose of this study was to determine if three SRIs affected sexual function in patients with an anxiety disorder or major depressive disorder over a 3-month period. Sixty-one patients were evaluated for at least 2 months in a prospective study of the effects of fluoxetine, sertraline, and paroxetine on five aspects of sexual function: libido, erection/lubrication, orgasm quality, orgasm delay, and sexual frequency. Measurements were made at baseline and at each month on visual analog scales. For men and women, orgasm quality was lower and orgasm delay longer at Months 1, 2, and 3 compared with baseline (p < .001). Erection scores were lower over time (p < .02) but this change was less dramatic. Lubrication, libido, and sexual frequency were not appreciably changed over 3 months. Anorgasmia was significantly more common in women than men at Months 1 and 2. Orgasm appears to be a primary sexual function affected by SRIs.