In 16 consecutive patients with clinically suspected and biochemically proven X-linked adrenoleukodystrophy (X-ALD), total delay (interval between onset of symptoms and diagnosis) and specialist delay (interval between referral to a specialist and diagnosis) were determined. All patients previously were unaware of the existence of X-ALD in their families. From the time of onset of symptoms attributable to this disease until diagnosis, mean total delay was 9.9 (range 1-33) years and mean specialist delay was 8.4 (range 0-33) years. Three patients who presented with adrenocortical insufficiency had mean total and specialist delays of 17.3 (range 9-33) years. Five patients with an initial diagnosis of multiple sclerosis had mean total and specialist delays of 12.8 (range 5-25) and 11.2 (range 1-23) years, respectively. In 12 patients with adrenomyeloneuropathy--the second most frequent phenotype of X-ALD--mean total delay was 11.0 (range 2-33) years and mean specialist delay 9.1 (range 0-33) years. Since 1981 X-ALD can be reliably diagnosed on the basis of elevated levels of very long chain fatty acids in plasma and/or cultured fibroblasts. The delays therefore must have been due to the unfamiliarity with the clinical manifestations and diagnostic possibilities of this disease. Once X-ALD is diagnosed, dietary treatment and/or bone marrow transplantation may be considered. Genetic counseling should be performed, and screening of other family members is essential for the early identification of affected relatives.