This paper analyzes the design and performance of hybrid automatic repeat request (HARQ) extensions to the multi- band orthogonal frequency division multiplexing (MB-OFDM) ultra-wideband (UWB) standard. It is shown how both Type-I and Type-III HARQ can significantly reduce the packet error rate (PER) in realistic frequency-selective channels. An exhaustive search is used to find an optimal low-complexity Type-III HARQ scheme by deriving the distance spectra and bit error upper- bound for all sets of complementary puncturing matrices. The consequences of selecting sub-optimal puncturing matrices are also quantified.