Optically impure tamsulosin including racemic tamsulosin can be resolved into optically pure (R)- or (S)-tamsulosin by the use of diastereomeric sulfonate salts of tamsulosin in a fractional crystallization technique. Racemic tamsulosin free base is a useful starting material for the resolution process and a method of obtaining the same in solid form, including two crystalline polymorphic forms, is also provided.