The evidence for the division of defenses measured with the Defense Style Questionnaire (DSQ) into immature, neurotic, and mature types appears to be lacking. We hypothesized that defenses can be represented unidimensionally. Classical multidimensional scaling was applied to the maturity ratings of items given by 279 experts. It appeared that the items of the DSQ can be represented unidimensionally. In a second study, two three-factor models of the DSQ were tested with confirmatory factor analysis, using scores of 543 psychiatric outpatients. Both three-factor models were implausible. A third study showed that the overall defensive functioning scores derived from the first study discriminated well between samples of 543 psychiatric outpatients, 69 medical students, and 68 graduate students attending a student counselor. We also found that the overall defensive functioning scores correlated positively with the current Global Assessment of Functioning in the psychiatric sample. We concluded that the DSQ is a useful instrument for measuring overall defensive functioning.