There is a perception that tamoxifen causes weight gain in breast cancer patients. The purpose of this research study was to determine if weight gain is associated with tamoxifen therapy and to observe the impact of weight gain on recurrence and survival. Prognostic indicators, changes in weight, and disease status from diagnosis to the end of treatment were studied in 200 consecutive Stage I and II breast cancer patients, not receiving systemic chemotherapy, admitted from 1986 to the present, with observation periods ranging from 3-5 years. A mean weight gain of 1.2 Kgs was seen in all patients; however, weight gain was not significantly different for those receiving tamoxifen vs. those not receiving tamoxifen, (P = 0.66, CI 95% for the difference -1.8 Kgs to +1.2 Kgs). Weight gain during treatment with tamoxifen was not correlated with treatment duration or with recurrence or survival. Age at diagnosis was positively correlated to weight gain in all groups. Our data failed to show that tamoxifen is associated with weight gain. The moderate weight gain observed in this patient population is comparable to the general aging disease-free population and may no be treatment-related. These findings may help to alleviate some concerns of both physicians and patients when tamoxifen is the drug of choice for adjuvant therapy.