Background Unbearable mental pain, depression, and hopelessness have been associated with suicidal behavior in general, while difficulties with social communication and loneliness have been associated with highly lethal suicide attempts in particular. The literature also links aggression and impulsivity with suicidal behavior but raises questions about their influence on the lethality and outcome of the suicide attempt. Objectives To evaluate the relative effects of aggression and impulsivity on the lethality of suicide attempts we hypothesized that impulsivity and aggression differentiate between suicide attempters and non-attempters and between medically serious and medically non-serious suicide attempters. Method The study group included 196 participants divided into four groups: 43 medically serious suicide attempters; 49 medically non-serious suicide attempters, 47 psychiatric patients who had never attempted suicide; and 57 healthy control subjects. Data on sociodemographic parameters, clinical history, and details of the suicide attempts were collected. Participants completed a battery of instruments for assessment of aggression-impulsivity, mental pain, and communication difficulties. Results The medically serious and medically non-serious suicide attempters scored significantly higher than both control groups on mental pain, depression, and hopelessness (p <.001 for all) and on anger-in, anger-out, violence, and impulsivity (p <.05 for all), with no significant difference between the two suicide attempter groups. Medically serious suicide attempters had significantly lower self-disclosure (p <.05) and more schizoid tendencies (p <.001) than the other three groups and significantly more feelings of loneliness than the medically non-serious suicide attempters and nonsuicidal psychiatric patients (p <.05). Analysis of aggression-impulsivity, mental pain, and communication variables with suicide lethality yielded significant correlations for self-disclosure, schizoid tendency, and loneliness. The interaction between mental pain and schizoid traits explained some of the variance in suicide lethality, over and above the contribution of each component alone. Conclusions Aggression-impulsivity and mental pain are risk factors for suicide attempts. However, only difficulties in communication differentiate medically serious from medically non-serious suicide attempters. The combination of unbearable mental pain and difficulties in communication has a magnifying effect on the risk of lethal suicidal behavior.