Sixty clinical isolates of Cryptococcus neoformans var. neoformans were analyzed by random amplification of polymorphic DNA (RAPD) using 12- to 22-mer primers in pairs. Five major profiles, which clearly distinguished between serotypes A (profiles I-III), AD (profile IV), and D (profile V), were identified. Forty-two of 58 serotype A isolates were assigned to profile I, 13 to profile II, and 3 to profile III. Profile I compromised 5 subtypes (profiles Ia-Ie), with 37 to 42 isolates in profile Ia. Twenty-seven of 28 isolates from patients with AIDS belonged to profile Ia (P<.001), as did 7 of 10 isolates from otherwise immunocompromised patients. Isolates from immunocompetent hosts were broadly distributed (profile I, 8 isolates; profile II, 10 isolates; profile III, 2 isolates). RAPD profiles were independent of body site and geographic origin of isolates. Isolates pairs from 3 patients produced identical profiles. A predominant genetic profile among serotype A strains from AIDS patients has not been reported previously.