Sulfonamide group drugs and their antimetabolite combinations are the most preferred drugs in the treatment and prophylaxis of Pneumocystis jirovecii pneumonia (PCP). Especially with the long-term use of trimethoprim-sulfamethoxazole (TMP-SMX) and dapsone, certain point mutations in the Pneumocystis jirovecii (P. jirovecii) dihydropteroate synthase (DHPS) gene are known to play an important role in the development of resistance. In the present study, we investigated the 165th and 171st nucleotide mutations in the DHPS gene in the P. jirovecii isolates from immunosuppressed and immunocompetent cases. P. jirovecii isolates from the bronchoalveolar lavage fluid (BALF) samples of 31 hospitalized cases and lung tissue samples of 37 autopsy cases were included in the study. For the analysis of wild-type and mutant genotypes, after the touchdown-PCR amplification method, the restriction fragment length polymorphism (RFLP) method was used. In this study, P. jirovecii DHPS gene was amplified in 28 of 68 (41%) of the samples. The RFLP method revealed that all the isolates in which the DHPS gene was amplified were considered as wild-type genotypes. To our knowledge, this present study is the first study in Turkey investigating P. jirovecii DHPS gene mutations associated with the sulfonamide resistance. All the isolates showed a wild-type pattern indicating that the occurrence of P. jirovecii DHPS mutations in Turkey is very low or absent.