OBJECTIVES: From tales of Christian tradition to essays of 17th century physicians, Friday has been identified as a day of ill luck. Amongst all Fridays of the year however the one coinciding with the 13th day of the month is known to be associated with extreme misfortune. Therefore, the fate of persons born on Friday the 13th (F13) warrants investigation. We investigated the effect of being born on Friday the 13th on the prevalence of a) cancer; b) diabetes; c) mental health disorders; and d) sexual disorders. METHODS: Persons born on Friday the 13th were identified from a drug utilization database. To control for seasonal variation and time-trends, persons born on Friday the 6th and Friday the 20th were selected as controls. Differences in prescription prevalences were analyzed using multivariate logistic regression. RESULTS: A total of 4202 cases and 8987 controls were identified. The number of cases was less than expected based on the number of controls (expected number 4396, P<0.01), suggesting a survival disadvantage for F13 cases. Age (32.8±22.6 vs. 32.7±23.0) and gender (53.1% vs. 53.3% female) were similar. Multivariable logistic regression showed no increase in prescription prevalences for F13 cases (P>0.1 for all drug classes). Exploratory analyses showed that F13 cases being prescribed antipsychotics were younger than controls (P=0.03) and diabetic cases were more often male (P=0.04). CONCLUSIONS: Although attenuating effects of survivor selection bias cannot be ruled out, the current study found no scientific basis for paraskavedekatriaphobia in relation to drug utilization. Significant differences in age and gender for specific subgroups may be attributed to the multiple comparison issue. Results will be presented on interaction effects of Friday the 13th coinciding with full-moon (n=154) and good Friday (n=113).