The Department of Laboratory Medicine at Asan Medical Center provides a special one-stop service to allow both doctors and outpatients to receive routine outpatient test results in a timely manner within 1 hr. We developed a new Laboratory Information System (LIS)-based monitoring system that records the laboratory turnaround time (TAT) in 3 phases and analyzes the time to complete each phase with relevant specimens. TAT is subdivided into preanalytical, analytical, and postanalytical phases based on the 4 time points when data are entered automatically into the LIS. The average TAT for 13,594 outpatient routine chemistry specimens with the one-stop service was 43.6±7.7 min. Completion times of the preanalytical, analytical, and postanalytical phases were 29.7±6.9, 13.9±4.1, and 0.02±0.13 min, respectively; 98.0% of the specimens were reported within 60 min. The remaining 2.0% were reported after 60 min with an average TAT of 68.7±11.3 min. Preanalytical phase delays were primarily responsible for the specimens reported between 60 and 90 min, and analytical phase delays were largely responsible for the few specimens (0.2%) reported after 90 min. For specimens reported between 60 and 90 min, the preanalytical phase was found to need improvement in order to shorten TAT; the main target for improvement was identified as the “waiting time for phlebotomy” step.