Sickle cell disease (SCD) exhibits itself in a broad spectrum of clinical behaviour ranging from a mild disease to an incapacitating condition. In this study, we have attempted to investigate the clinical diversity of SCD in different regions of Saudi Arabia. The results of haematological parameters and clinical manifestations in 41 children with SCD from the eastern province where the disease is mild, were compared with results obtained in 51 children from the south-western province (SWP), where the disease has been shown to be more severe. The severity index (SI) of patients from the eastern province ranged from 2 to 11 with a mean of 4.5 and in patients from the south-western province, the SI ranged from 2 to 18 with a mean of 9-5. In addition, the occurrence of hand and foot syndrome, vaso-occlusive crisis, and increased frequency of requirement of blood transfusion and hospitalization differentiated the clinical presentation of SCD in the patients from south-western province from those in the eastern province. Red blood cell level, total haemoglobin and packed cell volume were lower in the SCD children from the south-western province. Haemoglobin A2 level was significantly higher, while haemoglobin F, packed cell volume (PCV), mean corpuscular volume (MCV), and mean corpuscular haemoglobin concentration (MCHC) did not show any significant differences. HbF level did not influence the haematological parameters significantly in the SWP patients. It is concluded that the SCD in Saudi population is heterogeneous clinically and haematologically.