The influence of the moon phase on persons with mental disorders and the frequency of emergency and urgent admissions to the mental hospital in the city of Penza and Penza oblast (Russia) in 2018–2019 has been investigated. The frequency of hospital admissions is estimated among persons with severe mental disorders (with pronounced psychotic and pronounced affective and behavioral manifestations) during the periods of different moon phases: the full moon, new moon, first quarter, and last quarter. According to the results of the study, it has been found that the frequency of admissions did not differ significantly in the different moon phases (
p
= 0.4382), which agrees with the data of similar international studies.