The 16 Personality Factor Questionnaire (16 PF) was administered to 188 inpatients (87 women) in 3 groups in a mixed drug misuse-alcoholism facility: 68 patients whose primary substance of misuse was alcohol (mean age 34.9), 70 polydrug users (hallucinogens, amphetamines and barbiturates, mean age 30) and 50 who had used heroin and were in a methadone program (mean age 26.9). All were tested within 10 days of admission, and none were in severe states of withdrawal. Statistical analysis showed that polydrug users and alcoholics were more shy and more easily threatened than the heroin group; all groups tended to be apprehensive, but alcoholics were more so; alcoholics were also more anxious than the other groups (significant in all cases to at least the .05 level). In an analysis of personality factors by age, older patients in general (usually in a straight line continuum by age) were more outgoing, more affected by feelings, less assertive, less expedient, more practical and conservative, less independent and more tense and anxious regardless of which drugs they used. An analysis by sex (regardless of age and drug use) showed only 1 significant difference: women were more poised than men. Differences between these groups, then, were dependent upon age, not sex or type of drug use.