Background: As a substantial proportion of people with suicidal thoughts does not receive treatment, the internet can be a utilized to reach more people who need support. Aims: To examine maintenance of effects of online self-help for suicidal thoughts at 3-month follow-up within the intervention group of a randomized controlled trial (of which between-group 6-week post-test results have previously been reported, showing a small effect of 0.28 for suicidal thoughts in favour of the intervention group), and to investigate acceptability of the intervention through participant evaluation. Methods: 236 adults with mild to moderate suicidal thoughts were randomized to the intervention (n =116) or a waitlist control group (n =120). Assessments took place at baseline, post-test (6. weeks later), and follow-up (3. months after post-test). This paper reports on the intervention group and follow-up assessment only. Results: Effects established at 6-week post-test were generally maintained at 3-month follow-up in the intervention group. Participant evaluation revealed that a majority thought their suicidal thoughts had decreased during the study, that adherence to the intervention was below average, and that levels of satisfaction were acceptable. Limitations: The control group could not serve as a comparator as they had received access to the intervention at post-test. Conclusions: Effects of online self-help for suicidal thoughts can be maintained for up to three months. Participant evaluation indicated that online self-help for suicidal thoughts is acceptable, but there is also room for improvement.