Several studies have suggested that the TLC after childhood asthma is increased compared wtih that in healthy subjects. The aim of this study was to assess whether TLC is increased after childhood asthma and whether this is associated with an increased growth of the lung during adolescence. During a mean period of 29 months we studied 53 patients and 106 healthy control subjects who were matched for sex, age, and standing height. The patients had had asthma for a mean period of 10 yr. We found that in asthmatics TLC was increased in both sexes by about 7% predicted compared with that in the matched control subjects. The growth of TLC in ml/yr during adolescence was less in patients; this can be accounted for by a delay in pubertal development. When corrected for the delay in growth of stature, growth of TLC in ml/cm in asthmatics was similar to that found in control subjects. These findings support the hypothesis of a developmental change of enhanced lung growth during childhood asthma; they do not support a mechanism with progressive loss of elastic recoil of the lung.