Objective The aims of this study were to explore if the ambulatory fludrocortisone suppression test (FST) was safe, accurate and cost‐effective. Context The diagnosis of primary aldosteronism (PA) remains time‐consuming and complex. The FST is used to confirm PA, but it is an in‐patient test due to potentially serious complications such as hypokalemia. In Stockholm, FST has been performed since 2005 as an ambulatory procedure. Design This is a retrospective study including all patients investigated with FST in four hospitals in Stockholm, Sweden, during 2005–2019. Patients/Measurements In total, 156 cases of ambulatory FST (FSTamb) and 15 cases of in‐patient FST (FSTin) were included. FSTamb and FSTin were compared regarding health costs, clinical characteristics and laboratory results. Results No difference was found in the outcomes of FSTamb and FSTin. No severe complications were reported in FSTamb patients. No difference was found in the median value for plasma potassium on Day 5 between the two groups. Only three patients (1.9%) in the FSTamb had to repeat the test due to incomplete intake of medications. FSTamb and FSTin were equally accurate. The cost of performing FSTamb was at least 50% lower compared with FSTin ($2400 vs. $5200 per patient). The time needed for FSTamb was 60 min of physician's time and 150 min of nurse's time which were lower than the 5 days in FSTin. Conclusions Ambulatory FST is safe and accurate and can be performed with significantly less healthcare costs compared to FSTin.