INTRODUCTION:
Medical residency is a high-demand training period associated with depression, anxiety, and stress. evidence from Iran is limited across specialties and residency years.We assessed prevalence and predictors of distress among medical residents in Tehran.

METHODS:
we conducted a cross-sectional online survey from 1 January to 28 February 2022 among residents from major universities in Tehran. participants completed the dass-21 and a demographic/workload questionnaire. chi-square tests examined bivariate associations. multivariable linear regression identified independent predictors of depression, anxiety, and stress.

RESULTS:
of 353 residents analyzed, 75.9% were female, and 58.1% were married. overall prevalence was 69.3 percent for depression, 63.2 percent for anxiety, and 64.6 percent for stress. first-year residents reported higher distress than senior residents. specialty differences were significant, with surgical residents showing the highest levels, followed by medical and paramedical specialties. in chi-square analyses, marital status, gender, number of children, living with children, housing situation, specialty type, residency year, previous psychiatric diagnosis, psychiatric admission, substance or alcohol use, and number of monthly night shifts were associated with at least one mental health outcome (p<0.05). in regression models, depression was independently associated with marital status, living with children, accommodation, specialty type, and stress. Anxiety was associated with marital status, residency level, psychiatric admission, substance or alcohol use, number of shifts per month, and stress. Stress was associated with depression, anxiety, psychiatric admission, substance or alcohol use, residency level, and marital status.

CONCLUSIONS:
Depression, anxiety, and stress were highly prevalent among medical residents in Tehran, with the greatest burden in first year and surgical trainees. modifiable factors, including night-shift load and specialty-specific pressures along with identifiable personal risk markers highlight priority targets for intervention. routine screening, confidential access to mental health care, workload optimization, and stigma-reduction strategies are urgently needed to support resident well-being and safeguard patient care quality.