While the influence of cognitive and linguistic capacities and the perceptual features of objects on word-learning skills in people with typical development (TD) are well understood, there is little evidence concerning these mechanisms in people with Down syndrome (DS). Using a preferential looking task, we examined the ability of 29 children with DS (mean mental age: 3.44 years) to identify familiar words, fast-map pseudowords to novel objects, retain word-object mappings, and extend these mappings to new objects of similar shape. We also contrasted their word-learning abilities to those of 26 two-to-five-year-olds with TD and examined how cognitive and linguistic skills and perceptual information influenced those abilities. Children with DS were found to have similar identification, fast-mapping, and extension skills as their peers with TD, but retained fewer word-object mappings. Greater retention skills are related to mental age, verbal scores, and greater perceptual differences between the target and surrounding objects. These results indicate that children with DS use the same word-learning mechanisms and are influenced by the same linguistic and perceptual processes as children with TD.