2-Oxotryptamine and its homo derivative undergo intramolecular Mannich-type cyclization with acetone and other ketones to give spiro[indole-3,3'-pyrrolidin]-2-ones and spiro[indole-3,3'-piperidin]-2-ones. A similar reaction with the bis-homologue of 2-oxotryptamine to yield spiro[azepane-3,3'-indol]-2'-ones was unsuccessful.