Adult sickle cell patients visiting the Department of Hematology of the Academic Medical Centre in Amsterdam were eligible for our study. Inclusion criteria were: high-performance liquid chromatography (HPLC) confirmed diagnosis of homozygous sickle cell anemia (HbSS), sickle-C disease (HbSC), HbSb 1 -thalassemia (HbSb 1 -thal), or HbSb 0 -thalassemia (HbSb 0 -thal), age 18 years or older and capable of filling in a questionnaire (Dutch or English). All data were collected during a routine outpatient clinic visit.