To examine the frequency and microbial pattern of pneumonia and its effect on survival in the current era of orthotopic liver transplantation (OLT). At the Mayo Clinic in Jacksonville, Fla, the medical records of consecutive patients who underwent their first OLT between February 1998 and January 2001 were retrospectively reviewed through the end of the first year posttransplantation. Of 401 study patients, 20 developed pneumonia; estimates of incidence with corresponding 95% confidence interval (CI) at 1 and 12 months were 3% (1%-5%) and 5% (3%-7%), respectively. Pseudomonas aeruginosa was the predominant microorganism identified (in 8 of 14 patients) during the first month after transplantation. Between the second and sixth months, 2 of the 4 cases of pneumonia were due to fungal infections of Aspergillus fumigatus. Cytomegalovirus was associated with Aspergillus in 1 patient. No other viral or Pneumocystis carnil pneumonia was diagnosed. There were only 2 cases of pneumonia between 7 months and 1 year after transplantation, neither of which was fungal. Approximately 40% (95% CI, 14%-58%) of patients with pneumonia died within 1 month after diagnosis. The relative risk of mortality in the first month after onset of pneumonia was estimated to be 24 (95% CI, 10-54), which is strong evidence of increased risk of mortality with pneumonia (P<0.001). Pneumonia appears to occur less often after OLT than previously reported but still has a substantial negative effect on survival. In the early period after OLT, P. aeruginosa continues to be the predominant organism causing pneumonia.