The monoorganotin hydroxide dihalide hydrates RSn(OH)Cl2 · H2O with R = i-butyl and i-propyl were investigated by an X-ray diffraction study. The crystal structure consists of dimeric units with a rhombic four-membered tinoxygen ring and octahedrally coordinated tin atoms. These molecules are bonded by OH ... Cl hydrogen bridges to chains which are linked to layers.