Drawing upon concepts derived from ego psychological and object relations psychoanalytic theories of individual development and from a depth group psychology, the present empirical study, a naturalistic field investigation, explored hypothesized relationships between aspects of patients' psychological boundaries and structural features of inpatient therapy groups. More specifically, patients were assessed in terms of their level (i.e., psychotic vs. borderline organization) and form (i.e., anaclitic vs. introjective) of psychopathology. Their perceptions of themselves and of their therapy groups were measured following participation in two kinds of small group treatment designed to differ in terms of degree of internal structuring. Findings, generally supporting the hypotheses, showed the anaclitic borderline patients, in particular, to be most sensitive to structural variations and most adversely affected by an impersonal and highly structured treatment climate. Theoretical and practical implications of these findings were discussed.