Little is known about the habitual daily masticatory activity of subjects with different vertical craniofacial morphology. The purpose of the present study was to compare the daily long-term muscle activity of short-face subjects with that of long-face subjects as assessed in their natural environment. Digital photographs of the facial profile were obtained from a sample of 300 subjects and the ratio between anterior total and anterior lower facial height was assessed (Vertical Facial Index: VFI). Fourteen long-face and 16 short-face subjects were selected from the opposite tails of the frequency distribution of VFI. Long-term masseter activity was monitored for 8 h d(-1) in the natural environment by means of portable one-channel electromyograph recorders over three working days. Assessments included calculation of the number of activity periods (APs) per h (N/h), their mean amplitude (Amean), and their mean duration (Dur). The maximal electromyogram activity did not differ significantly between the short-face and the long-face subjects. There was no significant difference between the two groups investigated in N/h, in Amean and Dur. The findings suggest that habitual activity of masseter muscle in the natural environment was not influenced by the vertical craniofacial morphology as assessed in the present study.