Aim A previous study reported that the oral health‐related quality of life (OHRQoL) of Japanese individuals dropped sharply as they reached old‐old age. The aim of present study was to explore the risk factors of OHRQoL by investigating the association of OHRQoL with oral indices, lifestyle and psychological distress. Methods A questionnaire survey was carried out to assess the OHRQoL, oral indices, lifestyle, and psychological distress of patients who were of ≥75 years of age and who regularly visited a dental clinic for maintenance. OHRQoL and psychological distress were assessed using the General Oral Health Assessment Index (GOHAI) and the General Health Questionnaire, respectively. The relationships between the GOHAI score and related factors were examined by non‐parametric bivariate and logistic regression analyses using a GOHAI cut‐off score of 45.0. Results A total of 187 old‐old patients with a mean age of 77.9 ± 3.0 years participated in the present study. The average GOHAI score was 50.8 ± 8.0. In the bivariate analyses, the average sleeping hours, use of sleep medication, Short Form 8‐Item Health Survey (SF‐8), General Health Questionnaire score, and the number of teeth present were significantly correlated with the GOHAI score. A logistic regression analysis showed that the number of teeth present, General Health Questionnaire and the use of sleep medication were associated with the GOHAI score. Conclusions The present study found that the OHRQoL was strongly associated with insomnia and depression. It is therefore suggested that oral healthcare professionals take general background information, such as the presence of insomnia and depression, into consideration to improve OHRQoL when they treat old‐old patients. Geriatr Gerontol Int 2017; 17: 893–897.