This study explored the relationship between restriction spectrum imaging (RSI) and diffusion kurtosis imaging. Regions of interest for suspicious lesions and background tissue were identified in four patients with PIRADS 5 lesions. Kurtosis was estimated using either the signal fractions obtained from the RSI fit or the cumulant expansion for the NMR diffusion signal. A strong relationship was observed between RSI-derived restricted signal fraction and RSI-derived kurtosis. The performance of these two metrics was comparable in discriminating between suspicious lesions and background prostate tissue, and both outperformed the cumulant expansion approximation to kurtosis.