Floods are among the most frequent phenomena leading to disastrous, long term social and economic impacts globally. On November 15, 2017, 24 people were killed and hundreds were left homeless in the vicinities of the towns of Mandra and Nea Peramos in Attica region, Greece, as a result of a catastrophic flash flood triggered by extreme rainfall. The impact of such events has been the focus of studies for years consistently indicating adverse effects ranging from short to long term, on post-disaster physical and psychological health. This paper explores the initial impact of extreme flash floods on communities in terms of psychological and physical health, by means of a self-report questionnaire. Findings are investigated in relation to demographic variables and vulnerability predictors. Self-reports differed prior and after the flash flood, with negative changes in both domains. Results indicated significant differences in both physical and physiological health by gender, age, marital and occupational status. According to Spearman's correlation coefficient, physical and psychological effects showed moderately positive correlations for most independent variables. Results indicate a need to align prevention, aid and intervention strategies in the recovery phase and address issues such as public awareness, information provision and post disaster coping strategies.