Considering the negative effects of secondary hyperparathyroidism (SHPT) in patients with chronic renal failure (CRF), the objective of the present study was to evaluate body composition changes using conventional and vector bioimpedance analysis in patients before and after parathyroidectomy (PTX). Twelve adult patients, mean age 43 center dot 4 (sd 12 center dot 7) years, were evaluated prior to and 6 months after PTX. Diets were assessed with 3 d dietary records, and mean energy, protein, calcium and phosphorus intake were estimated from these inventories. Weight, height, BMI and bioelectrical impedance were measured; and biochemical markers of nutritional status (albumin and total protein) and bone metabolism (calcium, phosphorus and intact parathyroid hormone) were determined. No significant differences were observed in mean energy, protein and phosphorus after surgery. There was a significant increase in calcium intake after PTX (382 center dot 3 (sd 209 center dot 6) mg to 656 center dot 6 (sd 313 center dot 8) mg; P < 0 center dot 05). Mean weight, BMI, conventional bioelectrical impedance measurements, total body fat, lean body mass and total body water were unaffected by surgery. However, the phase angle and reactance significantly increased after PTX (5 center dot 0 degrees (sd 1 center dot 4) to 5 center dot 6 degrees (sd 1 center dot 3); 44 center dot 1 (sd 15 center dot 6) Omega to 57 center dot 1 (sd 14 center dot 4) Omega, respectively). The high levels of intact parathyroid hormone before surgery had a negative effect on total body fat (r -0 center dot 69, P < 0 center dot 05). After PTX, the mean albumin significantly increased (3 center dot 9 (sd 0 center dot 4) g/dl to 4 center dot 2 (sd 0 center dot 6) g/dl; P < 0 center dot 05). PTX for SHPT is associated with certain changes in laboratory values, dietary intake and body composition. The latter is best seen with bioimpedance vector analysis.