5-(2-(4-(12-Benzisothiazol-3-yl)-1-piperazinyl)ethyl)-6-chloro-13-dihydro-2H-indol-2-one mesylate dihydrate (Ziprasidone mesylate dihydrate) (I) is new. (I) is in the form of lath crystals or needle crystals.

PROBLEM TO BE SOLVED: To prepare a ziprasidone composition having an easily handleable suitable ziprasidone particle size from free ziprasidone base or ziprasidone hydrochloride by the use of a conventional preparation method or device. SOLUTION: This ziprasidone composition comprises crystalline free ziprasidone base or crystalline ziprasidone hydrochloride particles having an average particle size of about

Compositions comprising crystalline ziprasidone free base or crystalline ziprasidone hydrochloride particles having a mean particle size less than 85 µm and a pharmaceutically acceptable carrier are substantially bioequivalent and can be used to treat psychoses such as schizophrenia.

Compositions comprising crystalline ziprasidone free base or crystalline ziprasidone hydrochloride particles having a mean particle size less than 85 .mu.m and a pharmaceutically acceptable carrier are substantially bioequivalent and can be used to treat psychoses such as schizophrenia.