Primary meningoencephalitis caused by Naegleria fowleri was documented in a 16-year-old male from Mexicali in the state of Baja California in Mexico. In August 1978, seven days after sustaining moderate head trauma while swimming in a shallow, stagnant irrigation ditch on a hot summer day, the patient presented an acute illness with severe headache, fever and convulsions rapidly progressing into a comatose state. Actively moving trophozoites were observed in the spinal fluid on admission. The patient died shortly after admission to hospital on the third day of symptoms. Post-mortem examination revealed a meningoencephalitis with extensive destruction, haemorrhage and numerous parasites involving structures of the posterior fossa. Immunoperoxidase strains of trophozoites in meningeal and cerebellar tissue were positive for N. fowleri KUL and negative for N. gruberi, N. australiensis and Acanthamoeba rhysodes. This appears to be the first documented case of the disease in Mexico.