Objective  To assess the effects of sustained aromatase inhibition in older hypogonadal men.

Design and patients  In a 1‐year randomized, double‐blind, placebo‐controlled trial, 88 men, aged 60 years and older with testosterone levels between 5·2 and 10·4 nmol/l on a single measure or between 10·4 and 12·1 nmol/l on two consecutive measures, and with symptoms of hypogonadism were recruited. Subjects received either anastrozole 1 mg daily or placebo.

Measurements  Changes in gonadal steroid hormone levels, body composition [by computerized tomography (CT) and dual X‐ray absorptiometry (DXA)], strength, prostate specific antigen (PSA), symptoms of benign prostatic hypertrophy (BPH), haematocrit and lipid levels were assessed.

Results  Testosterone levels increased from 11·2 ± 3·3 nmol/l at baseline to 18·2 ± 4·8 nmol/l at month 3 (P < 0·0001 vs. placebo) while bioavailable testosterone levels increased from 2·7 ± 0·8 nmol/l at baseline to 5·4 ± 1·7 nmol/l at month 3 (P < 0·0001 vs. placebo). Testosterone and biotestosterone levels peaked at month 3 and then declined by month 12 (though they remained significantly higher than baseline and greater than placebo). E₂ levels decreased from 55·8 ± 15·4 pmol/l at baseline to 42·2 ± 13·6 pmol/l at month 3 and then remained stable (P < 0·0001). Body composition and strength did not change, nor did PSA, BPH symptoms, haematocrit or lipid levels.

Conclusions  Anastrozole administration normalized androgen production in older hypogonadal men and decreased E₂ production modestly. These alterations did not improve body composition or strength.