The success of parallel computing in solving real-life computationally-intensive problems relies on their e#cient mapping and execution on large-scale multiprocessor architectures. Many important applications are both unstructured and dynamic in nature, making their e#cient parallel implementation a daunting task. This paper presents the parallelization of a dynamic unstructured mesh adaptation algorithm using three popular programming paradigms on three leading supercomputers. We examine an MPI message-passing implementation on the Cray T3E and the SGI Origin2000, a shared-memory implementation using cache coherent nonuniform memory access #CC-NUMA# of the Origin2000, and a multithreaded version on the newly-released Tera Multithreaded Architecture #MTA#. We compare several critical factors of this parallel code development, including runtime, scalability, programmability, and memory overhead. Our overall results demonstrate that multithreaded systems o#er tremendous potential for qui..