The aim of this study is to produce preliminary data about the validation of the "Naples-Questionnaire of Distress at Work" (nQ.DW). This inventory is a new assessment tool in order to evaluate the distress perceived in the working environment by means of the differentiation of the conditions linked to the mobbing from which related to organizational disfunction. The nQ-DW also measures the bio-psycho-social global effects of these two phenomena. The questionnaire has been administered to workers suffering of a psychopathological disturbance related to work distress and to a control group matched for the sociodemographic and working variables. The statistical analysis demonstrated a significant validity and reliability. The degree of internal coherence was satisfactory. The ROC curves allow the determination of a threshold value which allows to separate the workers subjected to mobbing and/or organizational stress from control-workers with an optimal reliability degree. The values of the area under the ROC curves show that the inventory has a high discriminating capacity. Future studies, based on a greater sample size, will be oriented to the analysis of the questionnaire by means of multivariate techniques like the factorial analysis.