A 3-month-old lion-tailed macaque (Macaca silenus) infant that died on 2 February 1985 in the Baltimore Zoo (Baltimore, Maryland, USA) due to fulminating Streptococcus pneumoniae meningitis had congested, edematous lungs, and thickened and congested brain leptomeninges with a grayish-yellow fluid within the subarachnoid brain space. From bacterial cultures made postmortem of the subarachnoid brain space fluid, cerebrospinal fluid, throat secretions, nasal secretions, and lung fluid, we isolated pure cultures of group B streptococci, alpha hemolytic S. pneumoniae, type 19F (capsular). We also isolated Staphylococcus aureus and S. hemolytica from antemortem nasal and throat bacterial cultures from all 13 animals of the M. silenus colony. Streptococcus pneumoniae meningitis in M. silenus has not been previously reported.