The literature on the psychological aspects of cancer has been critically reviewed under 4 main categories, and the following generalizations may be made: 1. Published studies suggest a slightly higher cancer death rate in hospitalized psychotic patients than in the normal population; the reason for this is obscure and may well be due to the inadequacy of the statistics. 2. The psychological reactions and defenses of persons to the development of cancer are reported to be similar to those found in neurotic patients. Particularly prominent are depression and a sense of guilt. 3. Some authors report the development of cancer secondary to emotional trauma, or believe that cancer appears in patients with specific immature types of personality. 4. One group reports that established cancer grows more slowly in less inhibited individuals. The methods used in these studies may be grouped into 4 basic types--anecdotal, interview and case history, sociological and demographic analysis, and psychological testing. Unfortunately most of the studies suffer from inadequacy of design, and consequently the reported findings are subject to question. Specific suggestions are made for future research in this field, specifically in regard to the selection of cancer patients, the nature of control groups, the nature of measuring instruments, terminology, and statistical analysis. It is hoped that adoption of such suggestions by future investigators will open the way for more fruitful and scientific research in this complex field.