To determine the risk factors of gestational diabetes mellitus in refugee populations in the Gaza Strip, a retrospective case-control study was performed between March and June 2011 in the United Nations Relief and Works Agency (UNRWA) primary health care clinics. Data were collected on maternal sociodemographics and the prevalence of diagnosed GDM according to World Health Organization criteria from clinics where postnatal Palestinian refugee women had been diagnosed with GDM during previous pregnancies, and non-GDM women were used as controls. Sociodemographic characteristics, pre-pregnancy body-mass index (BMI), obstetrics history and family history of diabetes were used as study variables. In total, 189 incident cases of GDM were identified. The most significant risk factors for GDM were: history of miscarriage more than once; overweight before pregnancy; history of stillbirth; history of caesarean birth; and positive family history of diabetes mellitus.