Abstract Initial retention of the mandibular denture was clinically observed and measured as both static and dynamic retention. There was strong evidence that retention of a mandibular denture might continue although the actual period of time could not be determined. Initial retention of the mandibular denture was considered the result of securing the firm relation of the denture to its supporting structures mainly by use of patient control of muscular activity as "proretentive" and stabilizing factors. Static and dynamic retention did show a clear interdependence. While static retention reached maximum values quickly, dynamic retention increased progressively in a period of 4 weeks and reached an optimum of approximately 60 per cent of the value of static retention for the corresponding period. In general, static retention was always higher than dynamic retention. The adjustment by the patients to new mandibular dentures as expressed by their own assessment was easily achieved during the 4 week period of this study.