An eight year old, castrated male shepherd mix presented for a total hip replacement. On presentation, the dog was extremely lame and uncomfortable. Significant physical exam findings included bilateral popliteal lymphadenopathy, generalized muscle atrophy, lingual ulcerations, and multiple enlarged and painful joints. Diagnostics pursued included a complete blood count, chemistry panel, urinalysis, urine culture, synovial fluid cytology and culture, thoracic radiographs, hindlimb radiographs, abdominal ultrasonography, and serology. Based on the results of these diagnostic tests, the dog was diagnosed with idiopathic immune-mediated polyarthropathy and severe coxofemoral osteoarthrosis. This paper uses this clinical case as a model to discuss a clinically relevant approach to diagnosing polyarthropathies in dogs. It includes a discussion on the categorization of polyarthropathies, as well as a brief overview of the individual disease processes.