The aim of the study was to identify the genetic background of retinitis pigmentosa in a Polish family with previously excluded involvement of the majority of known genes for this disease, except for the ORF15 exon in the RPGR gene (Xp21.1). ORF15 is a highly repetitive, purine-rich DNA region with a number of different polymorphic variants and thus difficult to study. Genomic DNA was isolated from peripheral blood of the family members (n = 9). ORF15 exon was amplified in a long-range polymerase chain reaction and sequenced using the next generation method. Presence of the identified variant was confirmed by direct Sanger sequencing of the amplicon encompassing the mutation. The NM_001034853:c.2899delG (p.E967Kfs*122) mutation was detected in the ORF15 region. It completely segregated with the disease in the studied family. The identified alteration is pathogenic and has already been found to cause retinitis pigmentosa. It is estimated that more than a half of RPGR mutations are located in the ORF15 region. In families with a suspected X-linked inheritance of retinitis pigmentosa and in males with a negative family history of the disease, genetic tests should begin with an analysis of the ORF15.