We evaluated hematological parameters in 375 Sicilian adults with Hb S trait: Hb S levels were 41.91 +/- 2.65% in males and 40.92 +/- 2.8% in females. RBC, MCV, PCV, MCH, MCHC and total hemoglobin levels were within the normal range. Only mean Hb A2 and Hb F levels were increased (Hb A2 = 2.78 +/- 0.2%; Hb F = 1.05 +/- 0.18%), although they remained inside the normal ranges when compared to healthy controls (Hb A2 = 2.48 +/- 0.19%; Hb F = 0.93 +/- 0.14%) (p less than 0.0005). We conclude that our population does not show the hematological abnormalities such as microcytosis and decreased Hb levels, observed in the Black, Indian, Saudi Arabian carriers, and that the presence of those abnormalities is probably related to the coexistence of alpha-thalassemia, rarely observed in Sicily.