We compared the impact of a conditioning regimen with BU (n=16) or fractionated TBI (n=42) on height growth during adolescence and final height (FH), in 58 adults transplanted for acute leukaemia before adolescence (younger than 9 for girls and 11 for boys, and prepubertal). Heights were measured at three key periods, that is, transplantation, before adolescence, and FH, and compared using height standard deviation score (SDS) and cumulative change in SDS. The influence of the conditioning regimen was assessed using multiple linear regression and adjusting for gender, central nervous system irradiation, age and leukaemia status at transplant and type of transplantation. Overall mean height SDS was near normal at transplantation and before adolescence (0.2+/-0.1 and -0.2+/-0.1, respectively), but decreased to -1.6+/-0.1 at FH. There were significant differences between the TBI and BU groups when comparing FH SDS (-1.8+/-0.2 vs -0.8+/-0.2, P=0.001), mean change in height SDS from transplantation to FH (-2+/-0.1 vs -1.1+/-0.2, P=0.002) and mean change in height SDS during adolescence (-1.6+/-0.1 vs -0.7+/-0.2, P=0.003). We conclude that preparations involving BU, although less toxic than TBI-containing regimens, also have adverse effects on growth, predominantly during adolescence.