Background: Telephone hotlines are a widely used type of suicide prevention program. Aims: The aim of this study was to clarify the risk factors for suicidal ideation by investigating its association with a number of characteristics among telephone hotline callers. Method: Data were collected over a 10-year period from a total of 246,595 calls to Inochi No Denwa, a telephone crisis hotline in Ibaraki, Japan, and subsequently analyzed. Odds ratios for suicidal compared with nonsuicidal ideation were also calculated. Results: About 6% of the calls to the hotline were suicide related, and about 2% of the callers had attempted suicide in the past. Odds ratios for suicidal ideation increased during winter, but no daily tendencies were evident. Those whose problems were related to their way of life were at the highest risk of suicidal ideation, followed by those with health-related concerns. Conclusion: We were able to identify risk factors for suicidal ideation based on an analysis of enormous amounts of data from a telephone crisis hotline in Japan. Knowledge of these risk factors is expected to lead to improvements in suicide prevention programs.