This study constitutes the first molecular analysis of hereditary angioedema (HAE) in Greece, where 11 patients from three unrelated families with recurrent angioedema attacks and decreased C1 inhibitor antigenic levels were analyzed for SERPING1 mutations. Interestingly, one family displayed a novel SERPING1 alteration, characterized by the substitution of two consecutive nucleotides TC to AA, resulting in a termination codon (F225X). To the best of our knowledge, this is the first report of such a mutation in SERPING1, causing HAE. The second family displayed the nonsense mutation W482X, and the third the missense mutation M1V, already described in the literature. The type of mutation did not predict clearly the disease phenotype, since even members of the same family displayed a variety of the frequency and the severity of angioedema attacks. Our study identified a novel mutagenesis mechanism for HAE pathogenesis, providing additional evidence for the genetic heterogeneity of the disease.