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Glucocorticoids (GCs) reduce inflammation and preserve muscle function in boys with Duchenne muscular dystrophy (DMD) but cause pubertal delay. Pubertal induction with testosterone is recommended but longer-term outcome is unknown. Objective: To assess hypothalamic–pituitary–gonadal axis, muscle volume and function 5 years after pubertal induction. Methods: A prospective observational follow-up of a clinical study was conducted. 15 GC-treated males with DMD were treated with incremental testosterone for 2 years (end of regimen +2 years) then evaluated at +2.5 years and +5 y ears (final follow-up ~3 years after last injection). Data collected included testicular volume (TV), gonadotrophin, testosterone, inhibin B, muscle function, and limb muscle MRI. Results: Participants were 18.7 years (s.d. 1.6) at the final follow-up and had been on GC for 11.2 years (s.d. 2.2). Testosterone levels were similar at +2.5 years (8.6 nmol /L (s.d. 3.4) and 5 years (11.0 nmol/L (s.d. 6.1). TV increased from 2.8 mL ( s.d. 0.9) at +2 years to 7.1 mL (s.d. 1.8) then 10.6 mL (s.d. 3.5) at +2.5 years and +5.0 years (P < 0.001). Inhibin B levels increased from 55.6 pg/mL (s.d. 47.0) at baseline to 158.2 pg/mL ( s.d. 87.6), P =0.004 at 5 years but remained lower than reference values (mean 305 pg/mL). Muscle contractile bulk decreased. Interpretation: Pubertal induction with testosterone in DMD is associated with HPG axis activation and ongoing increases in inhibin B, TV, and testosterone concentrations. Some patients have normal levels which is promising regarding future fertility. Given the beneficial impact of testosterone on bone health, muscle, and well-being, monitoring testosterone levels in this population and supplementation of sub-optimal levels is important.