The reaction of 1-alkyl- or 1-arylsulfonyl-3-alkylthioureas (I) with carbonyl chloride or phosphoruspentachloride afforded the previously unreported sulfonylcarbodiimides. When the reaction was conducted at room temperature, the intermediate 1-alkyl- or 1-arylsulfonyl-3-alkylchloroformamidines (III) were isolable.