Azithromycin isopropanolate of the empirical formula azithromycin:[H.sub.20].sub.x:[isopropanol].sub.y is obtained from the crystallization of azithromycin in isopropanol and water. The x and y values is confirmed by single X-ray diffraction determination. In one embodiment x=1.5 and y=0.25. In another embodiment x=0.75 and y=0.5.