In order to evaluate the interfemoral variability of bone mineral density (BMD) in patients receiving thyroxin (T4) replacement therapy, dual-energy X-ray absorptiometry (DXA) was performed on both hips and the lumbar spine of 114 individuals. BMD was measured in 47 patients under T4 therapy in suppressive doses because of histologically proven thyroid cancer and 67 age-matched controls free of any known local or generalized disorder that would affect the bones and joints. Variation in BMD between both hips was determined for four different regions of interest, i.e., Ward's triangle, intertrochanteric region, trochanter, and femoral neck. No significant difference in hip BMD was found between patients and controls. Even though some individuals had large interfemoral BMD variation, no significant difference in hip BMD variability between the groups was observed. In patients under suppressive T4 replacement therapy, BMD measurement in one hip is suitable to predict BMD of the other hip and therefore unilateral hip measurement may be adequate.