Background: Waiting time is a common problem in pharmacy units. This shows that there is still waste. Lean hospital approach is a methodology that believed to reduce or eliminate waste so it can make quality services. Research Objectives: To identify critical waste and the root causes of critical waste in the outpatient pharmacy unit of Wates State Hospital. Method: Case study research with a qualitative approach. The stages of the research was the observation of service processes mapped through value stream mapping, questionnaires to obtain critical waste, interviews with the 5why method to find out the root of the critical waste. Results and Discussion: The results of value stream mapping obtained nonconcoction prescription services with lead time of 1 hour 4 minutes and value added ratio of 8,6% while concoction prescription services with lead time of 1 hour 12 minutes and value added ratio of 7,6%. Waste waiting is a critical waste with a percentage of 24,4%. The root causes of waste waiting are the length of use of hospital management information system server, limited number of human resources and influenced by layout factors and the flow of service process. Proposed improvements include short, medium and long term proposals. Conclusion: Waste waiting is a critical waste in the Outpatient Pharmacy Unit of Wates State Hospital with the proposed improvement applying the 5S method, optimizing service with the number of available human resources, changing the flow of prescription work based on a more efficient and effective layout and replacing the new hospital management information system server. Keywords: Lean Hospital, Outpatient Pharmacy Installation, Waste Waiting