In the majority of hypertensive patients, no particular cause for abnormal blood pressure is evident (primary or essential hypertension). In contrast, in the minority of patients with secondary hypertension a specific underlying cause is responsible for the elevated blood pressure. The prevalence of secondary hypertension is higher in patients with resistant hypertension than in the general hypertensive population and increases with age. The list of secondary forms of hypertension is long and prevalence of the individual causes of secondary hypertension varies. Hence, this review divides them into two categories: common causes and rare causes. If appropriately diagnosed and treated, patients with a secondary form of hypertension might be cured, or at least show an improvement in their blood pressure control. Consequently, screening for secondary causes of hypertension plays an essential part in the care of patients with arterial hypertension. If the basal work-up raises the suspicion of a secondary cause of hypertension, specific diagnostic procedures become necessary, some of which can be performed by primary care physicians, while others require specialist input.