Alkaptonuria is a rare autosomal recessive genetic disorder that causes accumulation of homogentisic acid (HGA) due to loss of homogentisate 1,2-dioxygenase (HGD) activity. Large amounts of HGA excreted in the urine turn the urine dark upon exposure to air. Deposition of HGA polymers, which are oxidized into a melanin-like pigment, discolors and degenerates connective tissues and also leads to ochronosis. The most common clinical consequence of HGA polymer deposition is ochronotic arthropathy, which does not differ in clinical presentation from other degenerative arthropathies. The disease not only involves joints, but also the spine, kidney, and cardiovascular system. We report a case of ochronotic arthropathy that was misdiagnosed as traumatic joint arthritis in the right knee. The patient was informed that data concerning the case would be submitted for publication, and he provided consent.