Introduction Previous studies have demonstrated increased suicide rates on holidays such as New Year, nationally and internationally. Comparable to New Year's Eve, Swedish Midsummer is a major holiday, linked to high levels of alcohol consumption in the population. We, therefore, hypothesized that suicides and deaths with undetermined intent would increase during the Midsummer celebration. Methods We used a retrospective death registry design to investigate all suicides that occurred on Midsummer's Eve (ME), Midsummer's Day (MD) and 28 adjacent days (AD) during 1980-2018. Data were stratified by diagnosis type, sex and age, and was analyzed with paired t-tests, Poisson regression, and time-series charts with 95% confidence intervals. Results During the 30-day investigation period, the observed average was 4.3 deaths per day (23.3% cases with undetermined intent). ME, but not MD, was associated with significantly fewer suicides compared to AD (-1.08 deaths, p < .01). ME, but not MD, was simultaneously associated with more deaths with undetermined intent (+0.58 deaths, p = .007). No moderating sex or age effects were found. Descriptive statistics showed that poisonings, drownings and traffic-related injuries were common among the undetermined ME cases. Discussion The study found that suicide decreases and deaths with undetermined intent increases on ME. The findings are interpreted considering that substance use may affect both suicidal intentions and diagnosis classifications. Social and cultural support and holiday anticipations might also account for suicidal behaviors on ME.