The aim of this quasi-experimental study was to examine the effectiveness of a telephone support intervention 1 week after surgery on the quality of life (QOL) of patients with breast cancer. The sample consisted of 228 patients with breast cancer allocated to an intervention group (n = 120) and control group (n = 108). The data were collected using Ferrans and Powers Quality of Life Index-Cancer Version (QLI-CV) and European Organization for Research and Treatment of Cancer Quality of Life Questionnaire Breast Cancer Module (EORTC QLQ-BR23). The self-reported QOL of patients with breast cancer was considered moderately high. Statistically significant associations were found between QOL and the demographic characteristics of age, education, and employment status and of having underage children. Statistically significant associations were found between QOL and clinical characteristics such as type of surgery and axilla treatment. The strongest predictors of poor QOL were age, control group, and type of surgery. Age was the strongest predictor of poor QOL in global QLI and in the health and functioning, socioeconomic, and family subscales. The patients' experiences show that the telephone intervention was helpful and the timing was appropriate. The QOL in patients with breast cancer was better in subscales of body image, future perspective, and postoperative side effects. The intervention group showed significantly better body image; they worried less about the future and had less postoperative side effects than the control group did. These results may help in discussing QOL issues and should be considered when planning and implementing interventions for patients with breast cancer.