The exonic regions of the carnitine palmitoyltransferase 2 (CPT2) gene were characterized from 101 patients with defined clinical and biochemical evidence for the adult onset form of CPT II deficiency and in 2 patients detected as newborns with abnormal acylcarnitine profiles. Twenty-seven disease-causing mutations within the CPT2 gene were identified in this cohort, 16 of which were novel. A total of 60 disease-causing mutations have been identified to date in CPT2 and 41 of these are predicted to produce amino acid substitution/deletions. The implications of these mutations are described in light of recent advances in our understanding of the molecular structure of members of the carnitine acyltransferase family.