Autosomal dominant familial dysalbuminemic hyperthyroxinemia (FDH)is characterized by modified human serum albumin (HSA) inducing asubstantially higher affinity for thyroxine (T4). Histidin or prolinsubstitution on residue R218 produces localized conformationalchanges of HSA creating additional room for T4 binding, leadingto 14-20 fold normal total T4 (TT4) levels. Affected individuals areconsidered euthyroid. Our patient is an 18 months-old swiss girl bornto a mother known for the rare R218P mutation in the HSA gene.She presented with severe failure to thrive (height -2.92 SD, weight-3.6 SD), habitual hip dislocation without anatomical anomaly, latefontanelle closing and protruding ears. Psychomotor development isslightly retarded. Thyroid function testing confirmed extremely high TT4(1446.0 nmol/l) levels, which are similar to her brother's values (1534.4nmol/l and 1757.6 nmol/l respectively). Free T4 seems slightly elevated(26 pmol/l), probably due to methodological reasons. TSH (0.92 mU/l),free T3 (4.4 pmol/l) and thyroxin binding globulin (32 mg/l) are withinthe normal range. Her two half-brothers, affected by the samemutation, are now 18.7 (P1) and 16.6 (P2) years old and wereoriginally described by S. Pannain et al. in 2000. Both werecharacterized by growth retardation (-2.1 and -2.2 SD) before the ageof 4 years. P1 has reached a normal adult height (-0.4 SD) and P2has caught up to normal growth (-0.68 SD) with moderate bonematuration delay. Pubertal development and anterior pituitary functionare adequate. Primary growth and developmental retardation in thefirst years of life with adequate catch-up seem to be a distinctcharacteristic in FDH with R218P mutation. Hip dislocation is typicallyseen in other situations associated to thyroid disorders, like Downsyndrome. These findings might be explained by altered early thyroidhormone utilization in children with FDH.