Glucose tolerance and the behaviour of cortisol during an oral glucose tolerance test (OGTT) was investigated in 126 patients with adrenal "incidentalomas" (age: > 45 years) and in 129 age-matched controls. Impaired glucose tolerance (IGT) was found to be more common (p < 0.02) among patients with adrenal incidentalomas. Subdividing these patients by their body weight it was found that 29% (controls: 25%) of those with normal body weight (BMI 20 - 25 kg/m2) had IGT/DM. In overweight (BMI 25 - 30 kg/m2) and obese patients (BMI 30 - 40 kg/m2) the share of IGT/DM was 32% (controls: 19%) and 66% (controls 42%), respectively. The prevalence of a "paradoxical" rise in serum cortisol concentrations during the OGTT was slightly higher (p < 0.05) among patients with adrenal incidentaloma than among controls. Patients as well as controls with this abnormal behaviour of cortisol were characterized by lower basal serum cortisol concentrations (p < 0.01) but no association was seen with either the presence of IGT or with post-dexamethasone concentrations of serum cortisol. Thus both in patients with and without adrenal incidentalomas abnormal glucose tolerance is an age- and weight-dependent phenomenon unrelated to the post-prandial behaviour of serum cortisol concentrations.