Objectives: There is a lack of research into online mindfulness drop-in sessions (OMDIS) that have been offered freely to the public, especially during the Covid-19 pandemic. These sessions offer more flexibility than standard mindfulness-based interventions that run for a set number of sessions, as individuals can ‘drop in’ to as many sessions as and when they like. This research aimed to explore the impact of attending group facilitated OMDIS on psychological outcomes in the general population. Methods: A quantitative cross-sectional retrospective design was adopted in this study. Participants (n=112) were recruited online through OMDIS providers in the UK and internationally. Attendees were asked to complete an online survey with measures of depression, anxiety, distress and wellbeing, both for their current state and retrospectively for their state before attending any OMDIS. They also reported the number, duration and frequency of sessions attended, as well as their ease and accuracy of retrospective recall. Results: Paired T-tests and two-way repeated measures ANOVAs were conducted. Findings indicated that: OMDIS were efficacious in improving depression, anxiety, distress and wellbeing; attending more sessions, more frequently, for longer durations was not required to attain these benefits; and being on a psychology waitlist or having prior mindfulness experience did not lead to greater benefits, whereas having depression prior to attending OMDIS did lead to greater improvements in psychological outcomes. Conclusions: The current study is the first to explore and provide evidence for the efficacy of OMDIS on psychological outcomes. OMDIS are cost-effective and readily available and therefore could be offered to those on waiting lists for psychological interventions, who often wait prolonged periods without any support. Further research is needed to understand other factors that may impact efficacy in order to maximise the utility of OMDIS. Keywords: Online, mindfulness, drop-in, mental health, depression, anxiety