We propose an efficient multicast cell-scheduling algorithm, called multiple-slot cell-scheduling algorithm, for multicast ATM switching systems with input queues. Cells in an input-queueing system are usually served based on the first-in-first-out (FIFO) discipline, which may have a serious head-of-line (HOL) blocking problem. Our algorithm differs from previous algorithms in that we consider the output contention resolution for multiple time slots instead of the current time slot only. Like a window-based scheduling algorithm, our algorithm allows cells behind an HOL cell to be transmitted prior to the HOL cell in the same input port. Thus, HOL blocking can be alleviated. We have illustrated that the delay-throughput performance of our algorithm outperforms most of those algorithms that consider only the output contention resolution for the current time slot. We also present a simple and efficient architecture for realizing our algorithm, which can dramatically reduce the time complexity. We believe that the proposed architecture is very suitable for multicast asynchronous transfer mode (ATM) switching systems with input queues.