Abstract: The present invention relates to pharmaceutical compositions containing the antifolate aminopterin, processes for making the compositions, and methods of using them to treat disorders in adult and pediatric patients. Pharmaceutical compositions substantially free of impurities are provided comprising a therapeutically effective amount of aminopterin, or a pharmaceutically acceptable salt thereof. Relative to the teachings of the prior art, the disclosed methods and compositions provide unexpected improvements that include a greater interpatient oral bioavailability in pediatric patients, a smaller interpatient coefficient of variation of oral bioavailability, a smaller mean intrapatient coefficient of variation of oral bioavailability, a greater therapeutic index, a smaller coefficient of variation of toxicity, efficacy in combination therapy, and efficacy of certain polyglutamated metabolites.