Autosomal dominant polycystic kidney disease (ADPKD) is the most frequently occurring hereditary kidney disease, and axial spondyloarthritis (SpA) is one of the most frequently occurring rheumatic diseases. Treatment-related decisions for axial SpA may pose a challenge in case of renal involvement. The authors describe two siblings with cooccurrence of these two diseases. The association of these two diseases is not well known. Practitioners should monitor renal function in SpA patients and take treatment-related decisions regarding renal involvement. Antitumor necrosis factor-alpha (anti-TNF-α) agents may be used in case nonsteroidal anti-inflammatory drugs (NSAIDs) cannot be utilized.