The coronavirus disease 2019 (COVID-19) pandemic and quarantine measures have raised concerns regarding their psychological effects on populations. Among the general population, university students appear to be particularly susceptible to experiencing mental health problems. To measure the prevalence of self-reported mental health symptoms, to identify associated factors, and to assess care seeking among university students who experienced the COVID-19 quarantine in France. This survey study collected data from April 17 to May 4, 2020, from 69 054 students living in France during the COVID-19 quarantine. All French universities were asked to send an email to their students asking them to complete an online questionnaire. The targeted population was approximately 1 600 000 students. Living in France during the COVID-19 quarantine. The rates of self-reported suicidal thoughts, severe distress, stress, anxiety, and depression were assessed using the 22-item Impact of Events Scale-Revised, the 10-item Perceived Stress Scale, the 20-item State-Trait Anxiety Inventory (State subscale), and the 13-item Beck Depression Inventory, respectively. Covariates were sociodemographic characteristics, precariousness indicators (ie, loss of income or poor quality housing), health-related data, information on the social environment, and media consumption. Data pertaining to care seeking were also collected. Multivariable logistic regression analyses were performed to identify risk factors. A total of 69 054 students completed the survey (response rate, 4.3%). The median (interquartile range) age was 20 (18-22) years. The sample was mainly composed of women (50 251 72.8%) and first-year students (32 424 47.0%). The prevalence of suicidal thoughts, severe distress, high level of perceived stress, severe depression, and high level of anxiety were 11.4% (7891 students), 22.4% (15 463 students), 24.7% (17 093 students), 16.1% (11 133 students), and 27.5% (18 970 students), respectively, with 29 564 students (42.8%) reporting at least 1 outcome, among whom 3675 (12.4%) reported seeing a health professional. Among risk factors identified, reporting at least 1 mental health outcome was associated with female gender (odds ratio OR, 2.10; 95% CI, 2.02-2.19; P < .001) or nonbinary gender (OR, 3.57; 95% CI, 2.99-4.27; P < .001), precariousness (loss of income: OR, 1.28; 95% CI, 1.22-1.33; P < .001; low-quality housing: OR, 2.30; 95% CI, 2.06-2.57; P < .001), history of psychiatric follow-up (OR, 3.28; 95% CI, 3.09-3.48; P < .001), symptoms compatible with COVID-19 (OR, 1.55; 95% CI, 1.49-1.61; P < .001), social isolation (weak sense of integration: OR, 3.63; 95% CI, 3.35-3.92; P < .001; low quality of social relations: OR, 2.62; 95% CI, 2.49-2.75; P < .001), and low quality of the information received (OR, 1.56; 95% CI, 1.49-1.64; P < .001). The results of this survey study suggest a high prevalence of mental health issues among students who experienced quarantine, underlining the need to reinforce prevention, surveillance, and access to care.