Diuretics are commonly used for the treatment of hypertension. Yet, hypokalaemia is a well-recognised adverse effect. We conducted a retrospective study to evaluate the incidence of severe hypokalaemia, defined as requiring hospitalisation, among patients on indapamide. We searched a territory-wide database, Clinical Data Analysis and Reporting System of the Hong Kong Hospital Authority. We traced all hypertensive patients who had been prescribed indapamide in 2007-2016 and all admissions due to hypokalaemia in 2007-2018. Factors associated with hospitalisation were studied using multivariable logistic regression. During the period studied, 62,881 patients were started on indapamide and 509 (0.8%) were hospitalised for hypokalaemia. 53% of these hospitalisations occurred within the first year of treatment, and half of those in the first year occurred during the first 16 weeks. Female sex (adjusted OR, 1.75; 95%CI, 1.45-2.12) and immediate-release formulation (adjusted OR, 1.41; 95%CI, 1.14-1.75) were associated with hospitalisation. In the multivariable model, advanced age was not a significant predictor. There were no deaths during hospitalisation and the median length of hospital stay was one day. In this large population-based study with 147,319 person-years of follow-up, severe hypokalaemia requiring hospitalisation was uncommon among hypertensive patients on indapamide. The risk is higher in women and in the initial weeks and months after starting therapy. The use of the sustained-release formulation reduces the risk. We conclude that using indapamide to treat hypertension is safe, even in the elderly, especially if the sustained-release formulation is used and electrolytes are monitored periodically.