The probabilities that children and adolescents alter their positions to non-adjacent canals (decanalization) on the current NCHS growth charts have been estimated. In this context, canals are the zones between the major percentile levels (5th, 10th, 25th, 50th, 75th, 90th, and 95th) that are shown on the charts. These probabilities were calculated for one- and 2-year intervals, beginning at each annual age from 3-16 years, using serial data for weight and stature from 329 male and 303 female participants in the Fels Longitudinal Study. The probabilities of particular types of decanalizations, categorized by the initial canal and the direction of the change in relative level (decrease/loss; increase/gain) are presented. The probabilities for 1-year intervals were very low and, therefore, they are not presented. Additionally, probabilities were calculated for transitions from the canal between the 5th and 10th percentiles to the zone below the 5th percentile and from the canal between the 90th and 95th percentiles to the zone above the 95th percentile. Both these transitions are shifts to levels that are outside the normal range, and are more common than decanalization. The probabilities of decanalization and of transitions from the normal range were generally larger for weight than for stature except for transitions from the canal between the 90th and 95th percentiles to the zone beyond the 95th percentile. The probabilities for both weight and stature tended to be larger for changes toward the medians than for changes from the medians. Decanalizations that involved increases in level were significantly related to advanced skeletal maturation at ages younger than the usual age of peak height velocity and to retarded skeletal maturation at ages older than the usual age of peak height velocity. Am. J. Hum. Biol. 10:351-359, 1998. ยฉ 1998 Wiley-Liss, Inc.