Objective: To investigate whether a referral letter to general physician given in workplace health checkup increased clinical follow-up rate in the employees who detected grade II or III hypertension. Design and method: We conducted a cluster randomized controlled trial at a retail company in which every employee who works for more than 6 hours a day had annual health checkup. A total of 107 supermarket stores were randomly assigned to the control arm (outpatient visit was recommended by a leaflet as usual) or the intervention arm (outpatient visit was recommended by a referral letter to a general physician together with the leaflet). Employees who met the following eligibility criteria were enrolled: (i) BP > = 140/90 mmHg in 2016, (ii) BP > = 160/100 mmHg in 2017, and (iii) not receiving medication in 2017. The primary outcome was the presence of clinical follow-ups for hypertension in outpatient visit within six months after the health checkup, which was assessed using health insurance claim data. Odds ratio (OR) and 95% confidence interval (CI) for the presence of clinical follow-ups in the intervention arm compared with the control arm was estimated using multilevel logistic regression, accounting for the store's level effect. Study protocol was registered at the University Hospital Medical Information Network Clinical Trials Registry (UMIN-CTR, ID = 000025411) Results: We analyzed 273 participants (mean age was 50.3 years, 55% women) from supermarket stores (control: 135 patients in 52 stores, intervention: 138 patients in 55 stores). Mean systolic blood pressure (standard deviation) was 165 (10) mmHg in the control arm and 164 (10) mmHg in the intervention arm. Clinical follow-up rate was 19.3% (24/135) in the control arm and 34.1% (47/138) in the intervention arm. OR and 95% CI for the presence of clinical follow-ups in the intervention arm compared with the control arm was 2.33 (1.12–4.84). Conclusions: Among employees who detected grade II or III hypertension at their health checkups, giving a referral letter to a general physician on the day of the health checkup increased the clinical follow-up rate within six months.