A group of six girls with slowly progressive idiopathic precocious puberty (IPP) and a good initial height prognosis was followed without treatment. At first observation the girls had a bone age advance over chronological age of no more than 18 months, a delta height age (delta HA): delta bone age (delta BA) ratio higher than 0.9 and height prognosis was unimpaired after 6 months. During the first two years of follow-up the girls maintained an acceptable height potential. The delta HA:delta BA ratio remained constant at greater than 0.9. Predicted height showed a slight increase or decrease (+/- 4 cm). The girls were reevaluated after the age of 14 years and followed-up until they reached their final height (FH). The mean FH (155.4 +/- 2.8 cm) was below the mean target height (159.3 +/- 4.2 cm) by 3.9 cm (range -2.1 to -6.7 cm); this difference was not statistically significant. The FH was more than 5 cm below the target height in only one case; this girl had the most precocious onset of puberty, at 6 years of age. In three cases FH was between the 3rd and 10th centiles. These three girls had a target height below 158 cm (< 25th centile). Girls with slowly progressive IPP and a good initial height prognosis preserved height potential with an acceptable final height without therapy.