Abstract: A process for the hydroformylation of olefinically unsaturated compounds whose hydroformylation products are insoluble or only sparingly soluble in water, comprising reacting the olefinically unsaturated compounds at 60.degree. to 180.degree. C. and 1 to 35 MPa with carbon monoxide and hydrogen in a homogeneous phase in a polar organic solvent and in the presence of a catalyst system comprising a rhodium carbonyl compound and a salt of a sulfonated or carboxylated organic monophosphine or polyphosphine, which salt is soluble both in the polar organic solvent and in water, distilling off the polar organic solvent from the reaction mixture and separating the catalyst system from the distillation residue by extraction with water.