Abstract: A waste collection assembly is provided, whereby urine and excrement from a bedridden patient can be collected without lifting or moving the patient, and without soiling the underlying mattress. The assembly comprises a mattress pad having an elongated layer of cushioning material and a central cavity disposed therein. The cavity is enclosed and supports a bed pan assembly therein. The bed pan assembly comprises an enclosed container, a flexible and replaceable waste collection bag, and a securement ring that secures the bag to the container. The container is disposed within the cavity, while the mattress pad covers the mattress. This allows waste to be collected without moving the patient or exposing the mattress to contaminants. Further provided is a cavity plug of cushioning material that can secure over the cavity when the bed pan assembly is not in use.