Screening scales can be useful in searching for common mental disorders in primary care and in tracking relevant prevalence and correlates in community surveys. However, it is important to document their validity, before using them. We developed Italian versions of the widely-used K10 and K6 screening scales following the WHO forward-translation and back-translation protocol. To evaluate their effectiveness as screens for DSM-IV 12-month mood or anxiety disorders and “serious mental illness” (SMI), the scales were validated in a two-stage clinical reappraisal survey. In the first-phase, the scales were administered to 605 people. In the second-phase, a sub-sample of 147 first-phase respondents over-sampling screened positives was administered the 12-month version of the Structured Clinical Interview for DSM-IV Axis I Disorders as a clinical gold standard. Performance of the scales in screening for chosen disorders was assessed by calculating area under the receiver operating characteristic curve and stratum-specific likelihood ratios. Both the K10 and K6 performed well in detecting DSM-IV mood disorders, anxiety disorders, and serious mental illness (SMI), with areas under the curve (AUCs) (95% CIs) between 0.82 (0.75–0.89) and 0.91 (0.85–0.96). The Italian versions of the K6 and K10 scales have good psychometric properties, making them attractive inexpensive screens for mood disorders, anxiety disorders, and SMI.