PURPOSE: Comorbid medical conditions are common among breast cancer survivors, contribute to poorer long-term survival and increased overall mortality, and may be ameliorated by weight loss. This secondary analysis evaluated the impact of a weight loss intervention on comorbid medical conditions immediately following an intervention (12 months) and 1-year postintervention (24 months) using data from the Exercise and Nutrition to Enhance Recovery and Good health for You (ENERGY) trial-a phase III trial which was aimed at and successfully promoted weight loss. METHODS: ENERGY randomized 692 overweight/obese women who had completed treatment for early stage breast cancer to either a 1-year group-based behavioral intervention designed to achieve and maintain weight loss or to a less intensive control intervention. Minimal support was provided postintervention. New medical conditions, medical conditions in which non-cancer medications were prescribed, hospitalizations, and emergency room visits, were compared at baseline, year 1, and year 2. Changes over time were analyzed using chi-squared tests, Kaplan-Meier, and logistic regression analyses. RESULTS: At 12 months, women randomized to the intervention had fewer new medical conditions compared to the control group (19.6 vs. 32.2 %, p < 0.001); however, by 24 months, there was no longer a significant difference. No difference was observed in each of the four conditions for which non-cancer medications were prescribed, hospital visits, or emergency visits at either 12 or 24 months. CONCLUSIONS: These results support a short-term benefit of modest weight loss on the likelihood of comorbid conditions; however, recidivism and weight regain likely explain no benefit at 1-year postintervention follow-up.