Recent reports of mammoplasia during selective serotonin re-uptake inhibitor (SSRI) therapy suggested that this side effect may be more common than previously reported. We examined 59 women receiving > or = 2 months treatment with an SSRI or venlafaxine for changes in breast size in relation to menopausal status, weight gain and duration of drug therapy. Serum prolactin, estradiol and beta-hCG were also measured before and during treatment in a subgroup of patients. Twenty-three out of 59 patients (39%) reported some degree of mammoplasia. Significantly more SSRI vs. venlafaxine patients reported mammoplasia (p < 0.01). Eighty-four percent with mammoplasia had weight gain vs. 30% without mammoplasia (p < 0.001). The rate of mammoplasia was unrelated to age, menopausal status or duration of treatment. Serum prolactin increased during treatment in the paroxetine subgroup (p < 0.03). In conclusion, antidepressant-induced mammoplasia may be more common than previously expected.