A study was carried out to determine the pattern of microbiological organisms causing community acquired pneumonia in adult patients admitted to Penang Hospital between November 1999 and August 2000. Altogether, 98 patients (64 males, 34 females) with a mean age (+/- S.D.) of 55.9 (+/- 19.0) (range 15 to 87) years were included in the study. Causative organisms were identified in 42 patients (42.9%). Mycobacterium tuberculosis was the commonest pathogen being identified in 15.3% of cases, followed by Klebsiella pneumoniae (7.2%), Pseudomonas aeruginosa (6.1%) and Staphylococcus aureus (5.1%). Streptococcus pneumoniae and Acinetobacter spp accounted for 3 cases each (3.1%) and Haemophilus influenzae, non-haemolytic Streptococcus, Mycoplasma pneumoniae, Salmonella typhi, Escherichia coli, Klebsiella spp and Pseudomonas spp for 1 case each (1.0%). Four patients (4.1%) had dual infections and no case of legionella pneumonia was found in this series.