Our objective was to determine if the All-Patient Refined Diagnosis-Related Groups (APR-DRGs) and other comorbidity scores correlate with pain level, functional abilities, and hospital cost after primary total joint arthroplasty (TJA). Three hundred three patients having TJA were evaluated with average follow-up of 21 months. Western Ontario and McMaster Universities osteoarthritis index, Short-Form 36, and Quality of Well-Being index were administered before and after surgery. The APR-DRG subclassification including severity of illness (SOI) subclass scores and risk of mortality (ROM), Charlson index, American Society of Anesthesiologist (ASA), Charnley score, length of stay, and hospital costs were reported. Patients in a higher SOI and ROM subclasses had a statistically significant decrease in functional outcomes scores, longer length of stay, and greater hospitals costs than those in lower subclasses. However, correlations of comorbidity categories with outcome scores were poor. The APR-DRG classification helps identify those individuals with worse function and is specially suited in identifying those patients who incur a higher hospital cost.