Point mutations of AML1 are uncommon and predominantly reported in a rare minimally differentiated acute myeloid leukemia (M0 AML). Few data exist regarding the frequency of AML1 mutations in non-M0 cases. We screened 284 consecutive adult Thai patients with de novo AML and found that 3.9% had AML1 mutations. The highest incidence occurred in M6. Six novel mutations were uniquely identified in non-M0 cases. Sixty-four percent of the non-M0 patients with AML1 mutations had coexisting genetic abnormalities including FLT3 mutation in 36%. Our study provides evidence to support the model of multiple co-operating events, which could also be critical in the development of leukemia in non-M0 AML patients with mutated AML1. The prognostic significance of these novel mutations remains to be determined.