Peroxisomal disorders are genetic diseases in which an impairment in one or more peroxisomal function(s) causes clinical and multiple biochemical abnormalities. Early recognition of the major peroxisomal disorders in which functional peroxisomes are virtually absent, leading to a generalised impairment of peroxisomal functions, is of utmost importance, as this will enable the prenatal diagnosis of these severe diseases in future pregnancies. Unfortunately, clinical recognition of these disorders can be difficult because of the aspecific and varying phenotypic presentation. We analysed the clinical characteristics in 40 patients suspected of having a peroxisomal disorder to identify specific clinical criteria for diagnosis. From this study we conclude that the combined presence of at least three major clinical characteristics (present in greater than 75% of the affected patients, including psychomotor retardation, hypotonia, impaired hearing, low/broad nasal bridge, abnormal ERG, hepatomegaly) and one or more minor characteristics (present in 50%-75% of the patients, like large fontanelles, shallow orbital ridges, epicanthus, anteverted nostrils, retinitis pigmentosa) warrants biochemical investigation of peroxisomal functions. Further prospective investigations will have to be done to evaluate these criteria.