Sleep quality is a well-studied aspect of overall health, especially for those who have other compounded health issues like dementia. This study identified what factors affected sleep quality among Thai people with dementia who attended an outpatient psychiatric department. While we considered factors associated with poor sleep quality, we discussed the impact that family relationship specifically has on sleep quality for this population. A cross-sectional study was conducted among 80 patient-caregiver dyads. All patients were assessed by the TMSE, a neuropsychiatric assessment (Thai Mental State Examination). The PSQI (Pittsburgh Sleep Quality Index) was administered and multiple factors affecting sleep were investigated through face-to-face interviews with each patient and caregiver dyad. Interviews were conducted by a psychiatric nurse at a hospital offering outpatient psychiatric care. A chi-square test, t test, Spearman correlation, Pearson's correlation, and logistic regression were applied to identify statistically significant associations. Overall, we found that the prevalence of poor sleep in our target population was 70%, with a high sleep score (8.14 +/- 4.20). Factors affecting sleep included mental health problems, night-time cough and urinary frequency, pain and fever during the night, sleep environment problems, and stimulant use (63.8%, 57.5%, 47.5%, 20%, and 7.5%, respectively). Other factors previously associated with poor sleep quality in other studies were not associated in this study. Those with perceived poor family relationships are at a 5.57 times greater risk for poor sleep than those with perceived good family relationships. On the contrary, those without mental health problems significantly decreased their overall risk for poor sleep. Further investigation into these associations should be studied. In conclusion, health-care providers are encouraged to consider the impact of family context on sleep quality for people with dementia.