The effect of Adenotonsillectomy on somatic growth was studied prospectively in 57, randomly selected children (31 boys, 26 girls), aged 5.03+/-1.32 (mean+/-1SD) years. The indication for surgery was adenotonsillar hypertrophy with or without recurrent infections. Weight, height, triceps skinfold thickness, and Body Mass Index were measured prior to the operation and 6-13 months afterwards. Weight was significantly improved following T&A in all children. The improvement in height was significantly only for children under 5 years. In an attempt to uncover the pathogenetic mechanisms, lactic acid, pyruvic acid, somatomedin-C (IGF-I), growth hormone(GH), insulin, glucose, pH, hemoglobin (Hbeta). and white cell count (WBC) were also determined in the last 18 children, prior to and 6-8 months post operatively. For the comparison of pre and post operative values the paired t test was applied. Although the values of GH and IGF1 did not significantly increase post-op the IGF-1/GH ratio increased, possibly indicating improved IGF1 generation. There was also a rise in Hbeta values and a lowering of WBC, probably reflecting the lower frequency of infections. All other metabolic indices did not change. In conclusion, linear grow post-Adenotonsillectomy improved in children aged <5 years and was associated with improved with IGF-1/GH ratio, increased Hbeta values and decreased in WBC.