Peroxisomal disorder phenotypes are the result of mutations that cause defective peroxisomal assembly or alterations in the import mechanism of peroxisomal proteins that lead to multiple peroxisomal dysfunctions, or the result of a peroxisomal enzymatic deficiency with a single peroxisomal dysfunction. With complementation analysis, 16 groups have been found. Assignment of the genetic defect has been described for some of the complementation groups. We describe the clinical evolution and follow-up over 10 years of a patient who belongs to complementation group 4, although he showed a milder clinical course. It has been found in fibroblasts different peroxisome populations, normal processing and expression of beta-oxidation PTS1 and PTS2 proteins, abnormal ALD protein distribution and normal plasmalogen biosynthesis; abnormal beta-oxidation metabolites have also been detected in serum. Ultrastructural studies in liver showed peroxisomal mosaicism as in fibroblasts. It has been taken into account that peroxisomal mosaicism may lead to variability in peroxisomal diagnostic parameters, making difficult the final diagnosis in these patients.