Clinical presentation of pneumocystis pneumonia (PCP) during immunosuppressive therapy for rheumatic diseases was compared between patients with rheumatoid arthritis (RA; n = 7) and those without RA (non-RA; n = 12) based on a chart review. Both RA and non-RA patients with PCP were treated with methotrexate (n = 7) combined with steroids (n = 6) and/or biologics (n = 4). RA-PCP patients were found to have a higher mortality rate than non-RA-PCP patients (3/7 vs. 0/12, respectively; p = 0.036) due to a later exacerbation of interstitial pneumonia and a higher presentation rate of diffuse pulmonary lesions (4/7 vs. 1/12, respectively; p = 0.036) despite lower mean levels of serum beta-D: -glucan (314 ± 214 vs. 1139 ± 1114 pg/ml, respectively; p = 0.02) that suggested a lower burden of Pneumocystis jirovecii. In conclusion, PCP in RA patients with existing pulmonary lesions may trigger subsequent progression to lethal interstitial pneumonia.