A description is presented of the mental organization of primitive personalities (American borderlines, British paranoid-schizoid), as well as a generic course of analytic therapy I have sometimes experienced with them. Their mental organization may be qualitatively rather than quantitatively different from that of less disturbed persons. The differences are mostly attributable to a rudimentary psychic differentiation and integration, and compensatory pathological relationships. This configuration is hypothesized to have a unique developmental course, originating from a combination of constitutional factors and adaptation to a pathogenic interpersonal environment. Failure to appreciate the qualitative differences between the minds of the analyst and his less disturbed patients, on the one hand, and the mind of the primitive personality, on the other, may lead the analyst to employ unsuitable modes of analytic intervention with unfortunate consequences.