This study compared the performance of 30 poor readers in the third grade with those of 30 average readers of the same age and 30 younger readers matched with the same reading level on phonological, visuo-perceptual, orthographic, and naming speed tasks. Individual data revealed heterogeneous profiles for the poor readers: six (20%) exhibited visual deficit; two (6.7%) had a single phonological deficit; and six (20%) had a double phonological and visual deficit. A naming speed deficit appeared, not as a single type, but in association with a phonological deficit (23.3%), a visual deficit (3.3%), or both (10%). These results suggest that Koreans' most significant reading problems lie in phonological awareness and in visual and naming speed processing. In particular, phonological and visual deficits are major independent risk factors in Korean reading impairments. (Contains 4 tables.)