The invention provides a biodegradable drug-eluting particle useful for the delivery of diagnostic or therapeutic agents. In certain embodiments, the drug-eluting particle of the invention comprises a biodegradable porous silicon body, a reservoir formed within the porous silicon body having at least one opening to an exterior of the body, wherein the reservoir contains a therapeutic or diagnostic agent, and an agent-permeable seal disposed over the at least one opening. The invention further provides a method for treating a patient to obtain a desired local or systemic physiological or pharmacological effect comprising administering a sustained release drug delivery particle of the invention. The invention also provides methods of fabricating a drug-eluting particle for releasing therapeutic agents.