In a prospective trial we studied 176 consecutive patients having a primary total hip arthroplasty to compare the quality of life before and after operation in non-obese and obese groups. We used a modified Harris hip score and the Rosser Index Matrix to generate these scores, and found that the median preoperative quality of life score for both groups was similar. During review, both groups showed a corresponding marked improvement in quality of life scores at one and three years. There was no statistically significant difference in the improvement in scores between the non-obese and obese groups. It appears that relative body-weight on its own does not influence the benefit derived from primary total hip arthroplasty.