In central precocious puberty (CPP), characterised by premature but otherwise normal puberty, the early onset of the pubertal growth spurt with increased height velocity results in premature epiphyseal closure with reduced final height. We examined the growth pattern in 11 patients (9 girls and 2 boys) with CPP treated with a long-acting gonadotropin-releasing hormone analogue (GNRHa). Every 28 days 75 micrograms of the GNRHa Triptorelin (Decapeptyl CR, Fa. Ferring) per kg body weight are given intramuscularly. We observed body height, height velocity, bone maturation (dBA/dCA) and predicted adult height in these patients for up to 4 years. Before treatment body height was markedly elevated (2.5 +/- 4.4 SD above the age appropriate mean); after two years of therapy it reached the normal range. Height velocity decreased significantly within the first six months of treatment and remained subsequently low (F = 7.59; p < 0.0001). In the first year on treatment bone maturation (dBA/dCA) dropped from 1.8 +/- 0.42 to 0.7 +/ 0.27 and in the second year to its lowest value of 0.3 +/- 0.13 (F = 2.35; p < 0.05). The predicted adult height increased from 154.5 +/- 4.0 cm at the beginning of treatment to 160.3 +/- 3.9 cm at the most recent follow-up examination. The present data indicate that treatment with a long-acting GNRHa markedly affects body growth in CPP by reducing height velocity and delaying bone maturation. The predicted adult height appears to increase, consequently.