The duration of puberty in girls is related to the timing of its onset. 
To observe the time lapse between the start of puberty and the advent of menarche in groups of girls maturing at different ages.  A sample of 163 girls subgrouped by pubertal onset at 9 (n = 22), 10 (n = 53), 11 (n = 54), 12 (n = 27), and 13 (n = 7) years of age.  Clinical follow-up from 10 to 17 years of age.  Onset of puberty was defined by the combined observation of mammary development on the Tanner scale and the height curve.  The date of menarche was recorded (month and year), and the time lapse was expressed as a function of the date of birth.  In the overall study sample, the duration of puberty was 1.96 +/- 0.06 years.  For the subgroups of girls starting puberty at 9, 10, 11, 12, and 13 years of age, the time lapse to menarche was 2.77 +/- 0.16, 2.27 +/- 0.16, 1.78 +/- 0.08, 1.44 +/- 0.10, and 0.65 +/- 0.09 years, respectively (p < 0.001).  The correlation coefficient (r) between the onset of puberty and its duration was r = -0.62 (p < 0.001), and that of age of pubertal onset versus age of menarche was r = 0.66 (p < 0.001).  The duration of puberty in girls depends on the timing of its onset; the earlier the onset of puberty the longer its duration.