Haematological and clinical characteristics have been examined in 30 patients with homozygous sickle cell (SS) disease, 28 with sickle cell-beta zero thalassaemia, and 21 with sickle cell-beta+ thalassaemia. The latter could be divided into three groups on their molecular basis and HbA levels, four subjects with an IVS-2 nt 745 mutation having 3-6% HbA (designated S beta+ thalassaemia type I), 14 subjects with an IVS-1 nt 110 mutation having 8-15% HbA (designated S beta+ thalassaemia type II), and three subjects with an IVS-1 nt 6 mutation having 20-25% HbA (designated S beta+ thalassaemia type III). Comparisons were conducted between SS disease, S beta zero thalassaemia, and S beta+ thalassaemia type II. Compared to SS disease, both thalassaemia syndromes had higher HbA2 levels and red cell counts and lower mean cell haemoglobin content (MCHC), mean cell volume (MCV) and MCH, and S beta zero thalassaemia had higher HbF and reticulocyte counts. Compared to S beta zero thalassaemia, S beta+ thalassaemia had a higher haemoglobin and MCHC. Clinically, persistence of splenomegaly was more common in S beta zero and S beta+ thalassaemia type II compared to SS disease. Few significant differences occurred between SS disease, S beta zero and S beta+ thalassaemia type II in Northern Greece suggesting that the 8-15% HbA in the latter condition was insufficient to modify the clinical course.