Fewer than 300 cases have been reported worldwide, mostly from Australia, United States, Great Britain, Czechoslovakia, Thailand, and Mexico. These cases typically occur during the summer months in warm, humid climates presumably because of warmer waters coupled with increased swimming activity. The incubation period between exposure and clinical manifestations ranges from 1 day to 2 weeks. Symptoms include an acute headache, nausea, vomiting, fever, neck stiffness, and photophobia. Alterations in taste and smell may occur initially because of involvement of the olfactory nerve. Confusion, agitation, hallucinations, seizures, and coma eventually develop. The disease course is rapid after symptoms start, and death occurs within 4 to 6 days. A high index of suspicion is required for diagnosis of PAM because it is indistinguishable from acute bacterial meningitis. The CSF mimics the CSF in acute bacterial meningitis except that Gram stain is negative. The concentration of erythrocytes in the CSF may correlate with the degree of necrosis and inflammation present. A wet mount of fresh CSF smear reveals motile trophozoites. Neuroimaging studies in these patients are nonspecific and may show normal findings, cerebral edema, or contrast enhancement of the basal cisterns and sulci. Polymerase chain reaction can detect amoebic DNA in CSF and brain tissue samples. These infections are nearly uniformly fatal, and only five survivors of PAM have been reported. The high mortality rate likely reflects the difficulty with diagnosis and the poor-to-marginal response to therapy. In many cases, the diagnosis is made after death. Therapy for PAM is amphotericin B IV or intrathecally with added doxycyline and rifampin for synergism. The optimal duration of treatment is not known, but at least 10 days is probably necessary.