BACKGROUND: Excess weight is a strong predictor of incident breast cancer (BC) and survivorship. A limited number of studies comparing strategies for promoting successful weight loss in women with remitted BC exist. PURPOSE: CASTLE was a pilot study comparing the effectiveness/feasibility of in-person and telephonic behavioral-based lifestyle weight loss interventions in BC survivors. METHOD: Fifty-two overweight/obese women (BMI = 25-45 kg/m(2)) with remitted BC (stages I-IIIa) who recently completed cancer treatment were assigned to either an in-person group (n = 24) or an individual telephone-based condition (n = 11). Both interventions focused on increasing physical activity and reducing caloric intake. The phase I intervention lasted 6 months. The in-person condition received 16 group-based sessions, and the telephone condition received intervention calls approximately weekly. Phase II lasted 6 months (e.g., months 6-12), and all participants received monthly intervention calls via telephone. RESULTS: Participants were predominately Caucasian (80 %) with a mean age of 52.8 (8.0) years and BMI of 31.9 (5.4) kg/m(2). Mixed models ANOVAs showed significant within group weight loss after 6 months for both the in-person (-3.3 kg +/- 4.4, p = 0.002) and the telephonic (-4.0 kg +/- 6.0, p = 0.01) conditions with no between group differences. During phase II, the in-person group demonstrated significant weight regain (1.3 kg +/- 1.7, p = 0.009). CONCLUSION: Our pilot study findings demonstrated that telephone-based behavioral weight loss programs are effective and feasible in BC survivors and that telephonic programs may have advantages in promoting weight loss maintenance.