Congenital Hypothyroidism (CH) is one of the most frequent endocrinological diseases in children; in Italy. Its frequency is 1/3047 healthy term infants. It's well known that Congenital Hypothyroidsm (C.H.) is associated with various congenital defects. There are few data in the literature on the relationship between the blood coagulation and platelet aggregation in Congenital Hypothyroidsm.

The purpose of our study was to evaluate blood coagulation and platelet aggregation in 22 children suffered from Congenital Hypothyroidsm who were followed at our Department. The patients started treatment with L- tiroxina, not later than the 45 th day of life.

When study started the average age was 60,5 months (range 14-189 months); hormone profile was the following: TSH media 1,77 mUI/ml (range 0,2-8,8 mUI/ml) e T4 media 12,5 μg%ml (range 5,0-24 μg%ml).

The echographie and/or thyroid scintigraphy proved: agenesia in 12/22 patients (54%), hypoplasia in 4/22 patients (18%) ectopia in 3/22 patients(14%) normal thyroid in 3/22 patients(14%).

Blood coagulation: one patient had a PTT Ratio= 1.24: for this reason we investigated and diagnosed Von Willebrand's Disease (F.VIII:C 58%; Ricof. 40%; FVIII R:Ag 50%; RIPA test decreased).

The remainig patients had normal coagulation tests.

Platelet aggregation: we noted hyperaggregation with the following inductors: arachidonic acid, adrenaline, ADP, collagen, ristocetin. No alterations in platelet aggregation in congenital hyperthyroidism is reported in the literature. For this reason we deem necessary to confirm these data in a larger number of patients as soon as possible.