Atopic dermatitis (AD) is a chronic, inflammatory, itchy dermatosis with periods of remissions and exacerbations. Social isolation and lockdown measures may cause increased stress which in turn may affect the skin condition of patients with AD. We aimed to investigate the impact of the COVID-19 pandemic on the course of AD and the mental health of adult patients with AD. The study was based on an anonymous online questionnaire. A total of 91 adult patients with AD participated in this survey. The study population consisted of 77 (84.6%) female and 14 (15.4%) male patients. The average age of patients was 28.3 years. Fifty-four respondents out of 91 (59.3%) noticed a worsening in the course of AD. Patients with worsened AD most often indicated exacerbating itching of the skin (92.6% of 54). Only 54 (59.3%) patients continued treatment as directed by the attending physician. Of those that did not, 13 (14.3%) took or applied fewer medications and 24 (26.4%) stopped taking or applying medications altogether. Of all respondents, 60 (65.9%) believed that their mental health had deteriorated and 11 (12.1%) patients developed suicidal thoughts during the COVID-19 pandemic. The results indicate that the COVID-19 pandemic had a negative impact on the course of AD among adult patients. Forced life changes, increased stress, and poor adherence to treatment may have been contributing factors. Increased stress may have also worsened the mental health of patients with AD, which in turn may have exacerbated AD.