Self-induceded and distinguished from conditions they may resemble. Review of the literature since 1965 indicates much more frequent reporting in recent years, but most health care providers are still not sufficiently aware of the common factitious disorder. Up to 5% of physician-patient encounters may be because of factitious disorders, but these are only suspected when the workup leads to contradictory findings. Laboratory tests are often the only definitive diagnostic method, and clinicians may not be familiar with current technologies. Some clinical clues are listed; heightened awareness and the need for early diagnosis are emphasized. Discordant laboratory results should raise the possibility of a factitious disorder. Sophisticated laboratory tests that can accurately assay very small amounts of specific hormones or foreign substances in body fluids facilitate the diagnosis. The primary physician can now confirm an initial clinical diagnosis of factitious disorder promptly and directly rather than only by exclusion. (Arch Intern Med. 1994;154:1690-1696)