Background: Overcrowding was observed in a maternity ward of a tertiary level referral hospital, which serves the Kampong Cham and Tbong Khmum provinces in Cambodia and was constructed by the Japanese Official Development Assistance program. This study aims to investigate the reasons for the congestion, and the functions of the maternity ward within the provincial health system.Methods: The trend in the number of deliveries was determined between 2007 and 2017, and the maternity bed occupancy rate in 2017 was calculated. At the maternity the numbers and proportions of deliveries were assessed in 2017, as well as within other public health facilities in each district. Information on the deliveries was obtained from the maternity and the Ministry of Health.Results: A marked increase in the number of deliveries at the maternity was observed after the inauguration of the new building; specifically, from 1522 births in 2007 to 4667 in 2017. Users from Kampong Cham (2782, 60%) and Tbong Khmum (1572, 34%) were dominant. The bed occupancy rate was 187%, and 52% of the occupancy was for normal vaginal births. More than 100 women came to the maternity from up to 75 km distance for vaginal delivery. Of the estimated number of births in the two provinces, 36% and 13% were conducted at health centres and district hospitals, respectively.Conclusions: The overcrowding was mainly caused by normal vaginal deliveries, and perhaps was due to the policy of self-referral and open choice of delivery location. Overcrowding hampers the standard functions of a referral hospital and can horizontally and vertically widen inequities among the population. Overcrowding of a facility can be aggravated by the construction of a modern tertiary level facility, made possible by external aid such as that by Japan. Deliberate assessment and planning are essential from the viewpoint of the district health system to maximise the effect of external assistance to low- and middle-income countries.