There is a need to assess the psychiatric morbidity that appears as a consequence of terrorist attacks. The General Health Questionnaire (GHQ) has been used to this end, but its psychometric properties have never been evaluated in a population affected by terrorism. A sample of 891 participants included 162 direct victims of terrorist attacks and 729 relatives of the victims. All participants were evaluated using the 28-item version of the GHQ (GHQ-28). We examined the reliability and external validity of scores on the scale using Cronbach's alpha and Pearson correlation with the State-Trait Anxiety Inventory (STAI), respectively. The factor structure of the scale was analyzed with varimax rotation. Samejima's (1969) graded response model was used to explore the item properties. The GHQ-28 scores showed good reliability and item-scale correlations. The factor analysis identified 3 factors: anxious-somatic symptoms, social dysfunction, and depression symptoms. All factors showed good correlation with the STAI. Before rotation, the first, second, and third factor explained 44.0%, 6.4%, and 5.0% of the variance, respectively. Varimax rotation redistributed the percentages of variance accounted for to 28.4%, 13.8%, and 13.2%, respectively. Items with the highest loadings in the first factor measured anxiety symptoms, whereas items with the highest loadings in the third factor measured suicide ideation. Samejima's model found that high scores in suicide-related items were associated with severe depression. The factor structure of the GHQ-28 found in this study underscores the preeminence of anxiety symptoms among victims of terrorism and their relatives. Item response analysis identified the most difficult and significant items for each factor.