Introduction: Non-operative management has successfully been practised for long in diaphyseal fractures of both bones of the leg. This study attempts to establish an acceptability criteria for plaster cast in order to predict future loss of reduction and its adequacy. Materials and Methods: A total of forty subjects were included as per inclusion-exclusion criteria. Gap and cast indices were calculated in the immediate post reduction phase and at third week follow-up visit. Results: The mean values of gap and cast indices in the immediate post-reduction phase were 0.35±0.220 and 0.99±0.08 respectively and at the third week follow-up the mean value for both the parameters in those without loss of reduction were 1.11±0.50 and 1.03±0.09 respectively and in those with loss of reduction were 0.84±0.44 and 1.01±0.06 respectively. Conclusion: Gap and cast indices are not informative in assessing adequacy of reduction in diaphyseal fractures of both bones of the leg.