Pneumocystis jiroveci pneumonia (PJP) is a much-feared complication of the use of immunosuppressive drugs. There is no current consensus on the indications for PJP prophylaxis in patients with rheumatological diseases who are receiving higher-dose glucocorticoid treatment over a prolonged period. The decision on whether or not to administer prophylaxis depends primarily on the Number Needed to Treat (NNT) vs the Number Needed to Harm (NNH) of trimethoprim/sulfamethoxazole (TMP/SMX) or other forms of prophylaxis. A recent retrospective study from South Korea supports the efficacy and safety of TMP/SMX for patients using ≥ 30 mg prednisone for > 1 month, especially in those with high-risk disease or other risk factors. Surveillance of regional and national PJP incidence, along with possible predictors, may help in gaining a better understanding of risk groups and in drawing up a regional, or preferably national, protocol.