2,5-Diformylfuran (DFF) was obtained by heating a solution of 5-(hydroxymethyl)furfural in DMSO. The addition of acids or salts improved the selectivity, especially if bromides were employed. Good yields of DFF were obtained with HBr or NaBr as the catalyst. One-pot procedures were developed from fructose, which led to DFF in medium yields. This transformation occurs through the formation of 5-(bromomethyl)furan-2-carbaldehyde followed by a Kornblum-type reaction. In the presence of bromide salts, the in situ formation of the catalyst involves the thermolysis of DMSO and the association of the resulting strong acids with the bromides.