The authors studied the relative prevalence of erythroid cytoskeletal protein defects and their relationship with the clinical course of Hereditary Spherocytosis (HS) in 39 Portuguese patients of North of Portugal (25 families). This study showed that, in the North of Portugal, HS is primarily due to anquirin deficiency (72%), followed by band 3 (20%). These findings are similar to the published data in other Caucasian populations. Anquirin primary defects have been difficult to diagnose before splenectomy, due to high reticulocytes counts.