Although there have been numerous reports concerning the incidence and risk factors for transfusion with knee and hip arthroplasty, there is no information available for shoulder arthroplasty. Therefore, the purpose of this study was to determine the incidence of transfusion in a consecutive group of patients undergoing shoulder arthroplasty and examine risk factors for a transfusion. Between January 1, 1998, and December 31, 2002, the senior author performed 407 consecutive primary shoulder arthroplasties. Risk factors analyzed included preoperative hemoglobin level, age, sex, diagnosis, and hemiarthroplasty versus total shoulder arthroplasty. The indications for transfusion and associated complications were also reviewed. The overall transfusion rate was 8.1% (33/407). The incidence of transfusion was significantly greater among women (13.6% [29/213]) in comparison to men (2.1% [4/194]) (P = .0002). The risk for transfusion was significantly greater for patients undergoing shoulder arthroplasty for sequelae of trauma (15.8% [9/57]) (P = .0048) and rheumatoid arthritis (13.8% [8/58]) (P = .0153) compared with osteoarthritis (4.6% [10/218]). Preoperative hemoglobin level was found to be a significant risk factor for the need for transfusion (P < .0001). The rate of transfusion for hemiarthroplasty (8.3% [9/108]) and that for total shoulder arthroplasty (8.0% [24/299]) were not significantly different (P = .9203). The data from this study suggest that the rate of transfusion for shoulder arthroplasty varies markedly by sex and diagnosis. This information may be used to more accurately predict the need for transfusion and tailor preoperative blood ordering accordingly.