OBJECTIVE: To investigate the effect of adjuvant breast cancer therapy on quality of life, and to evaluate the occurrence of dose delay or reduction by type of therapy. MATERIALS AND METHODS: The study population was drawn from patients treated by a major oncology center in Southern California. The inclusion criteria were: females 18 years old or older treated with adjuvant therapy, with stage I, II or III non-metastatic breast cancer. Participants were sent up to five surveys: one before treatment initiation, two or three (depending on the number of cycles) at regular intervals between treatments, and a final one 4 weeks after the end of the chemotherapy session. The survey contained two quality of life instruments: the SF-36 and the Breast Cancer Chemotherapy Questionnaire (BCQ). RESULTS: At the beginning of the chemotherapy course, 40 patients were prescribed CMF (48.2%), 24 AC (28.9%), 11 A-CMF sequential (13.3%), and 8 other regimens (9.6%). Average values for the physical component summary score (PCS) of the SF-36 did not vary over time, ranging from 42.1 to 46.1. The mental component summary score (MCS) had a peak at mid-point (48.1), while it stabilized to the initial value at the end of the therapy (46.8 vs. 46.5). Comparisons of the difference between the baseline quality of life scores and a summary measure of the subsequent scores among treatment groups were not significant. Correlation coefficients showed that, at each period, MCS score was highly correlated with the disease-specific BCQ score (correlation coefficients from 0.69 to 0.81, p=0.001). During the chemotherapy course, 32 patients experienced a dose delay, 12 a dose reduction and 9 prematurely terminated their chemotherapy regimen, with no difference among treatment groups. DISCUSSION: The MCS of the SF-36 was highly correlated with the disease specific instrument, while the PCS was not.