Summary Objectives X‐linked adrenoleukodystrophy is an important cause of Addison's disease in boys, but less is known about its contribution to Addison's disease in adult men. After surveying all known cases of X‐linked adrenoleukodystrophy in Norway in a separate study, we aimed to look for any missed cases among the population of adult men with nonautoimmune Addison's disease. Study design Among 153 adult men identified in a National Registry for Addison's Disease (75% of identified male cases of Addison's disease in Norway), those with negative indices for 21‐hydroxylase autoantibodies were selected. Additionally, cases with low autoantibody indices (48–200) were selected. Sera from subjects included were analysed for levels of very long‐chain fatty acids, which are diagnostic for X‐linked adrenoleukodystrophy in men. Results Eighteen subjects had negative indices and 17 had low indices for 21‐hydroxylase autoantibodies. None of those with low indices and only one of those with negative indices were found to have X‐linked adrenoleukodystrophy; this subject had already been diagnosed because of the neurological symptoms. Cases of Addison's disease proved to be caused by X‐linked adrenoleukodystrophy constitute 1·5% of all adult male cases in Norway; the proportion among nonautoimmune cases was 15%. Conclusions We found X‐linked adrenoleukodystrophy to be an uncommon cause of Addison's disease in adult men. However, this aetiological diagnosis has far‐reaching consequences both for the patient and for his extended family. We therefore recommend that all adult men with nonautoimmune Addison's disease be analysed for levels of very long‐chain fatty acids.