This study aimed to identify the behavioural pattern of psychological distress (PD) in the population of 18 to 65 years old people in Mashhad, Iran, using latent class regression and evaluate the related factors. PD is a unique emotional state with suffering in response to a stressor or specific need that leads to temporary or permanent impacts. Due to its negative effects on several features of life like the quality of life, health, performance and productivity of individuals, PD and its consequences are considered a public health priority. A cross-sectional study was performed on 425,286 individuals aged 18 to 65, who were referred to health centres in Mashhad, northeastern Iran in the first half of 2018. The information required for this study, including a checklist of demographic information and the six-item Kessler Psychological Distress Scale (K-6), was obtained from the Sina System. Latent class regression identified three latent patterns of PD in answering the questions of the K-6 questionnaire, including severe PD (14%), low PD distress (40%) and no PD (46%). Statistical variables of this study due to the results are considered as the following: women, illiterate people, unemployed and divorced people, individuals aged between 50 and 59 years and people with low weight were more likely to be in the severe PD class than in the no PD class. Although a small percentage of people were classified as severely disturbed, the findings showed a high rate of symptoms of distress and sadness even in the no PD class.