Utilizing national data on patient care provided by family practitioners, general internists, and subspecialists in internal medicine, this study examines the complexity of care provided by generalist physicians versus subspecialty physicians on a disease-specific basis. Limiting the analysis to "principal care" provided by office-based physicians, the study finds the complexity of care provided by cardiologists for heart disease and by endocrinologists for diabetes mellitus to be somewhat greater than that provided by family practitioners and general internists, though the magnitude of the differences is not large. For chronic obstructive pulmonary disease, however, pulmonary disease specialists are shown to provide care that is substantially more complex than that provided by their generalist colleagues. For all disease and specialties, hospital care is substantially more complex than ambulatory care.