Loneliness represents asignificant health risk and is associated with numerous mental and physical conditions. The aim of this paper was to describe the prevalence of loneliness in Bavaria before and during the COVID-19 pandemic with respect to socio-demographic attributes. Data sources were the German Ageing Survey (DEAS) and the Socio-Economic Panel (SOEP). Univariate statistical analyses were carried out for different socio-demographic attributes, such as age, gender, type of household, education, and financial resources. According to the SOEP, the proportion of adults who are often or very often lonely increased from 2.3% in 2017 to 16.2% in 2021. In 2021, women had ahigher prevalence of loneliness than men (21.0% vs. 11.3%), and younger adults had the highest prevalence of loneliness (18 to 25years: 31.7%) compared to the other age groups. During the COVID-19 pandemic, loneliness increased in almost every population subgroup in Bavaria. Further studies are needed to examine whether this development is temporary or represents along-term effect even after the measures to prevent the spread of COVID-19 have been lifted.