Twenty two patients with thalassemia major who received successful bone marrow transplantation (BMT) were followed to verify the impact of the transplant procedure on subsequent growth and development. The transplant preparative regimen consisted of busulphan and cyclophosphamide. Growth and endocrinological function were assessed during the first 4 years following BMT. At the time of transplant most patients showed growth retardation. The median difference between chronological age and bone age was -9.5 months for the boys and -8.5 months for the girls. Patients > 7 years old at the time of BMT showed a significant worsening of their growth delay at 48 months following BMT compared with 12 months before transplantation. Patients < 7 years at the time of BMT had their growth retardation constant over time span after transplantation. Moreover six of 11 younger patients showed an improvement of their growth delay compared with one of 11 older patients. The outcome of height standard deviation score at 24 and 48 months following BMT was strictly correlated with the level of serum transaminases and ferritin. Sixteen patients had impaired growth hormone secretion after a provocative test evaluated at 24 months after transplant. At 48 months there was no significant increase in the mean peak GH levels. This study confirms that the growth retardation of patients with thalassemia major is multifactorial.