© 2020 The two-year preparation for the National university entrance exams in Greece is one of the most trying periods in a young person's life, physically and emotionally. The present study reports the results from 442 last year senior high school students who completed an online survey (16-30 April 2020) concerning the lockdown impact on their mental health. Overall, the rate of positive screen for depression (PHQ-9 score ≥ 11) significantly increased from 48.5% to 63.8% and of those scoring within severe depression range (PHQ-9 ≥20) from 10% to 27%; for anxiety (GAD-7 score ≥ 11) increased from 23.8% to 49.5% and of those scoring within severe anxiety range (GAD-7≥17) from 3.8% to 20.5%. After taking sex and baseline (one month prior to the lockdown) levels of depression and anxiety into account, the level of lockdown experienced distress was predictive of depression and anxiety levels in time of home confinement, accounting for about 30% of variance in symptoms severity scores. Although our results may be subject to sampling and recall bias, the unexpectedly high rates of anxiety and depression warrant an urgent call to action aiming at mitigating and managing mental health risks of senior high school students in future waves of pandemic.