This study focused on the factor structure, invariance, reliability, and validity of two DASS versions: DASS-21 and DASS-9. Dimensionality was examined with Exploratory and Confirmatory factor analysis in 2271 Greek adults of the non-clinical population. Sample was split in three parts and the “3-faced construct validation method” was adopted. An EFA and a Bifactor EFA model were tested in the 20% subsample for both DASS-21 and DASS-9. Then, in the 40% subsample eleven CFA models were tested for DASS-21 and six for DASS-9 (using ICM-CFA, Bifactor CFA and ESEM). Optimal DASS-21 and DASS-9 models were successfully validated in the remaining 40% subsample (i.e. in a subsample of equal power). DASS-21 and DASS-9 showed strict measurement invariance across gender. Reliability (α and ω) and AVE convergent validity were adequate for both versions. Correlation analysis based on 10 different measures revealed a predominant uniform pattern of relations, similar for both versions. Considering all findings, the Greek versions of DASS-21 and DASS-9 are invariant, reliable and show construct and convergent validity.