Here is the report of 119 cases of meningoencephalitis caused by mumps in San Francisco in 12 years (1943-1955). Most cases are mild, with no complications, no neurological consequences, last less than 5 days, and rarely require hospitalization. Death due to mumps meningoencephalitis is a very rare phenomenon, and in the entire medical literature only 3 such cases have been described (including one out of these 119).