In the Netherlands the prevalence of diabetes mellitus is high among people originating from Suriname (especially Hindustans), Turkey and Morocco. The majority of these patients has an Islamic background and, consequently, participates actively in Ramadan fasting. Ramadan fasting, especially among patients with type 1 diabetes and type 2 diabetes patients with vascular complications, is associated with multiple risks. Therefore, Ramadan fasting should be discouraged to these high-risk groups. Muslims with diabetes are exempted from Ramadan fasting, when fasting may lead to harmful consequences. When a patient insists on participating in Ramadan fasting, the medication should be adapted to prevent hypoglycaemia. The patient should be seen 4 or 5 days after the start of fasting. Patients using insulin should monitor blood glucose weekly by day curve during the Ramadan.