The question whether psychological factors affect cancer development has intrigued both researchers and patients. This review critically summarizes the findings of studies that have tried to answer this question in the past 30 years. Earlier reviews, including meta-analyses, covered only a limited number of studies, and included studies with a questionable design (group-comparison, cross-sectional or semiprospective design). This review comprises only longitudinal, truly prospective studies (N=70). It was concluded that there is not any psychological factor for which an influence on cancer development has been convincingly demonstrated in a series of studies. Only in terms of 'an influence that cannot be totally dismissed,' some factors emerged as 'most promising': helplessness and repression seemed to contribute to an unfavorable prognosis, while denial/minimizing seemed to be associated with a favorable prognosis. Some, but even less convincing evidence, was found that having experienced loss events, a low level of social support, and chronic depression predict an unfavorable prognosis. The influences of life events (other than loss events), negative emotional states, fighting spirit, stoic acceptance/fatalism, active coping, personality factors, and locus of control are minor or absent. A methodological shortcoming is not to have investigated the interactive effect of psychological factors, demographic, and biomedical risk factors.