We report the case of a 55-year-old male with flexion contractures of the hips and the knees due to an isolated adrenocorticotropin (ACTH) deficiency, a rare cause of secondary adrenal insufficiency. The presenting symptoms and signs, the laboratory investigations and the treatment are described. The case description is followed by a brief overview of ACTH deficiency and its symptoms and causes. Our case is then compared with other case reports available in the literature. The aetiology of the flexion contractures in adrenal insufficiency is still unclear. The authors want to draw attention to adrenal insufficiency as the cause of unexplained flexion contractures.