To evaluate the ability of two graphologists and two practising internists not trained in graphology to differentiate letters written by subjects who have attempted to commit suicide by self-poisoning and healthy volunteers, we performed a maximal blind controlled study vs. healthy volunteers. Forty fully recovered patients who had attempted to commit suicide and 40 healthy volunteers wrote and signed a short letter or story not related to the parasuicide or their mental health status. The evaluators classified the 80 letters as 'suicide' or 'no suicide' in an intention-to-treat analysis. Letters expressing sadness were subsequently excluded for a per-protocol analysis. Correct diagnosis of suicide and of healthy controls was made in, respectively, 32 of 40 and 33 of 40 letters by the graphologists and in 27 of 40 and 34 of 40 letters by the internists. After the exclusion of 12 letters expressing sadness, the sensitivity, specificity, positive predictive value and negative predictive value were, respectively, 73, 88, 81 and 82% for the graphologists and 53, 89, 80 and 71% for the internists. Both classified the letters with significantly more effectiveness than chance (p < 0.001) with no statistically significant difference between the two groups of evaluators. We concluded that graphological analysis is able to differentiate letters written by patients who attempt suicide from those written by healthy controls. This technique shows an acceptable degree of accuracy and could therefore become an additional discharge or decision-making tool in Psychiatry or Internal Medicine.