Over the past 30 years, the striking improvements in the survival rates of patients with childhood cancers are due, in large part, to the use of aggressive treatment strtegies. These therapeutic modalities are associated with a variety of late complications that span a spectrum from minor and treatable to serious and occasionally lethal. Nearly one-quarter of the late deaths in survivors of childhood cancer can be attributed to a treatment-related effect, for example, a subsequent malignant neoplasm or cardiac dysfuntion. The risk of late death due to causes other than recurrence is greatest in survivors treated with the combination of chemotherapy and radiotherapy. Among the 650 survivors followed in the Long-Term Follow-Up Clinic at the Memorial Sloan-Kettering Cancer Center, the most common sequelae are endocrine complications, which are seen in 40% of the patients. Growth hormone deficiency, primary hypothyroidism and primary ovarian failure are the endocrine disorders observed most often.