Longitudinal data from 165 women diagnosed and treated for breast cancer were used to investigate if the relationship between optimism-pessimism and quality of life (QOL) is attributed to the appraisal and coping strategies. The women completed the Life Orientation Test-Revised (LOT-R), as a measurement of optimism-pessimism, the Mental Adjustment to Cancer (MAC) Scale, as a measure for coping, a VAS for appraisal and the EORTC QLQ-C30, as a measure for QOL at two time points: at diagnosis and 12-months after breast cancer surgery. Optimism-pessimism had both a direct and indirect influence on QOL. Two coping strategies were particularly strong mediators for the indirect influence: fighting spirit and hopeless/helpless. Optimists responded with fighting spirit, which had a positive effect on their QOL. On the other hand, pessimists responded with hopeless/helplessness, which had a negative effect on their QOL. The relationship between pessimism and QOL at time of diagnosis was also mediated by appraisal, such as threat. The two coping strategies remained fairly stable over the 12 months within the optimists and pessimists.The results suggest that the influence of optimism and pessimism on QOL appears to be mediated by coping both before and after treatment for breast cancer. Fighting spirit and hopeless/helplessness appear to reflect the characteristic coping strategies for optimists and pessimists.