Despite regular blood transfusion and desferrioxamine treatment, growth impairment and pubertal delay are commonly seen in children and adolescents with transfusion-dependent thalassaemia and sickle cell disease (SCD). We evaluated growth parameters and sexual maturation in a large cohort of children and adolescents with SCD (n = 110) and thalassaemia (n = 72) receiving nearly the same protocol of transfusion and chelation, and compared them with those for 200 normal age-matched children, 30 children with constitutional delay of growth (CSS), and 25 children with growth hormone deficiency (GHD). Before transfusion, haemoglobin concentration had not been less than 9 g/dl in the past 7 years; desferrioxamine was administered for 7-10 years, including by the intramuscular and subcutaneous routes, three times or more per week. The height standard deviation score (HtSDS), growth velocity (GV) (cm/yr), and growth velocity standard deviation score (GVDSD) of children and adolescents with thalassaemia and SCD were significantly decreased compared to normal children (p < 0.01). Forty-nine per cent of thalassaemic patients and 27 per cent of patients with SCD had HtSDS less than -2, and 83 per cent of thalassaemic patients and 67 per cent of SCD patients had HtSDS less than -1. Fifty-six per cent of thalassaemic children and 51 per cent of children with SCD had GVSDS less than -1. The GV of thalassaemic children was significantly slower than that for children with SCD. Children with thalassaemia and SCD had HtSDS and GVSDS comparable to those for children with CSS but higher than those for patients with GHD. Serum ferritin concentration was correlated significantly with the linear GV in all patients (r = 0.45, p < 0.001). The bone age delay did not differ among the three groups with thalassaemia, SCD and CSS, but the delay was significant in the group with GHD. The mid-arm circumference was significantly smaller in children with thalassaemia and SCD than in normal children. The triceps skin-fold thickness of patients with SCD was significantly decreased compared to thalassaemic and normal children. The upper/lower segment ratio was significantly lower in thalassaemic and SCD patients than in normal children. In thalassaemic patients between the ages of 13 and 21 years a complete lack of pubescent changes was present in 73 per cent of boys and 42 per cent of girls. Seventy-four per cent of the thalassaemic girls had primary amenorrhoea. Girls with SCD aged between 13 and 21 years had markedly delayed breast development and menarche. Twenty-five per cent of boys with SCD above the age of 14 years had absence of testicular development. Males with thalassaemia and SCD who had spontaneous testicular development had significantly smaller testicular volume than did normal controls. Short children with thalassaemia and SCD had significantly decreased serum insulin-like growth factor 1 (IGF-1) concentrations compared to children with CSS. Collectively, these data confirm the high prevalence of impaired growth and pubertal delay/failure in children and adolescents with thalassaemia and SCD. The aetiology of impaired growth includes the contributions of lack of pubertal growth spurt due to delayed/absent puberty, decreased synthesis of IGF-1 which might be secondary to a disturbed GH-IGF-1 axis and/or under nutrition, probably due to the hypermetabolic status of these children. It is suggested that newer protocols of treatment, in addition to optimization of transfusion and chelation requirements, should increase the caloric intake of these patients and properly manage their pubertal delay-failure in order to improve their adult height.