Patients with type 1 diabetes (T1DM) present lower serum free IGF and IGFBP-3 values than healthy people. T1DM patients often present with associated autoimmune diseases such as thyroiditis or coeliac disease, and over time they frequently develop proliferative retinopathy, neuropathy or nephropathy in different combinations. The aim of this study was to evaluate the effect of two associated autoimmune diseases or three diabetic complications on the serum free IGF-I or IGFBP-3 levels in T1DM patients, who also have a family history of T1DM. Design. 246 T1DM patients were enrolled, and then subdivided into groups according to diabetic complications or associated autoimmune diseases. Demographic and clinical data were recorded. Serum free IGF-I and IGFBP-3 levels were determined by IRMA. IGF-I and IGFBP-3 generally present correlated serum values as confirmed in this study. Those patients with autoimmune thyroiditis and coeliac disease presented with significantly lower serum values of IGFBP-3, whereas free IGF-I was significantly lower in patients with the different diabetic complications. Retinopathy presented a slightly significant reduction in serum free IGF-I, while neuropathy and nephropathy showed a more pronounced fall. The number of complications was related to progressively decreasing free IGF-I levels. T1DM family history was associated with lower serum free IGF-I concentrations. These findings were confirmed after correction for age, glycosylated haemoglobin levels, insulin treatment protocol, body mass index, serum creatinine and sex. Despite a direct correlation between serum free IGF-I and IGFBP-3, the correlation between the two molecules in patients with associated autoimmune diseases was lost, possibly due to different mechanisms of metabolic regulation.