Abstract An investigation has been made into the possible contribution of a superior labial frenum to the occurrence of a persisting midline diastema. Forty schoolchildren 8 to 9 years of age with prominent frenums and midline diastemas of more than 1 mm. were subdivided into two groups. One group was subjected to frenectomy; the other served as a control group. Two years after the start of the study the diastemal closure was significantly greater in the frenectomized group than in the control group. However, the difference in closure between the two groups was gradually reduced, and after 10 years there was no longer any significant difference.