A population-based study was conducted among residents of Rochester, Minnesota from 1935-1984 to examine the influence of diagnostic access bias on the incidence and mode of presentation of clinically recognized sarcoidosis. Immigrants had an elevated risk of sarcoidosis and were more likely to present with asymptomatic sarcoidosis diagnosed on routine screening chest radiographs. Similar patterns were observed for health professionals, a group with markedly greater access to the diagnostic procedures which label them as having sarcoidosis. Sarcoidosis exhibits a spectrum of manifestations, ranging from a totally asymptomatic process discernible only by specific diagnostic scrutiny to a clinically obvious presentation with significant morbidity. For disease entities such as this, apparent patterns of occurrence may depend on differential access in the study population to the maneuvers necessary for diagnosis. Diagnostic access bias, in addition to other diagnostic biases, deserves more careful scrutiny in epidemiologic research.