The intercycle variability in gait of two temporal parameters (stride time and double-support time) and the step-to-step variability of two spatial parameters (step length and stride width) were assessed in 64 healthy adults, 32 aged 21 to 47 and 32 aged 66 to 84. For all parameters the median values of the coefficient of variation did not differ significantly between the two groups. They were below 6% for step length and stride time but much higher for stride width and double-support time (between 17 and 27%). These differences in variability are discussed in relation to the control systems involved. Step length and stride time are thought to be determined predominantly by the gait-patterning mechanism, whereas stride width and double-support time may be determined predominantly by balance-control mechanisms. The results suggest that, in both age groups, the gait-patterning mechanisms are more consistent in their operation than are the balance-control mechanisms and that increased variability in gait should not be regarded as a normal concomitant of old age.