The Zung Self-Rating Depression Scale (SDS) is generally used to screen for the presence of depression. The purpose of this study was to investigate scores on the SDS, Japanese version, in undergraduates at Tsurumi University School of Dental Medicine in Yokohama, Japan. A total of 2,197 dental students completed the SDS from 2006 through 2008. The investigation took place each year over a 3-week period from June to July. When investigating, the Institutional Review Board at Tsurumi University approved the study. Students could voluntarily agree or decline to participate in the study, and all responses were provided anonymously. SDS scores by sex, class year, and change over time were analyzed. The mean SDS score ranged from 43.7 ± 8.5 to 44.8 ± 9.0 between 2006 and 2008. Women were significantly more depressed than men in 2007 and 2008. The SDS scores of the same students were high continuously for 2 years. "Diurnal variation," "personal devaluation," and "confusion" had the highest scores of the 20 individual items of the SDS. Of the participating students, 31.4-37.2% were classified as being moderately to severely depressed. Logistic regression analysis was used to compute the odds ratio for SDS scores of ≤47 versus ≥48. The item "suicidal rumination" had the highest chance of being associated with depressive symptoms in all 3 years. Although this research was limited to a single department of dentistry, it appears that dental students experience various levels of depression. Providing mental healthcare options to these students may be helpful.