Ninety-seven specimens of sympatric monkeys and apes from East Malaysia and 115 monkeys and apes from West Africa are examined in order to evaluate the magnitude and nature of the great ape-monkey linear enamel hypoplasia (LEH) 'dichotomy'. This study demonstrates that great apes from both regions have a higher incidence of LEH and repetitive LEH than do gibbons and monkeys. However, the authors find that the dichotomy is not as clear-cut as previous research suggests, since some monkey samples exhibit high LEH frequencies. The authors evaluate the potential influence of great ape-monkey differences in crown height on this dichotomy. They show that canine crown height variation is weakly associated with LEH variation. Differences between monkeys and great apes in their crown formation spans and in their experience of environmental stress may be more likely causes of the dichotomy.