Long term storage stable bendamustine-containing compositions are disclosed. The compositions can include bendamustine or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable fluid contains a mixture of PEG and PG an organic or inorganic compound in an amount sufficient to obtain a pH of from about 6.0 to about 11 for the polyethylene glycol, as measured using USP monograph for polyethylene glycol and optionally an antioxidant. The bendamustine-containing compositions have less than about 5% total esters, on a normalized peak area response ("PAR") basis as determined by high performance liquid chromatography ("HPLC") at a wavelength of 223 nm, after at least about 15 months of storage at a temperature of from about 5° C. to about 25° C.
