Background: Classification of acts of self-directed violence has been shown to be inadequate in past research. Furthermore, level of expertise have been shown to be unrelated to classification correctness. Aim: The aim of the present study was to investigate whether participants provided with a definition are more reliable in their judgment than participants without a definition. Method: Two hundred sixty-one participants (psychology students, psychotherapists-in-training) were presented with case vignettes describing different acts of self-directed violence and were asked to make a classification. On the basis of randomized allocation, half of the participants received a definition of the different acts of self-directed violence, whereas the others did not. Results: Overall, 24.9% of the cases were misclassified. The presentation of a definition was not accompanied by a higher classification accuracy. Limitations: There may be issues about the validity of the case vignettes. Conclusions: The results highlight the importance of more methodological training of psychologists regarding suicidal issues.