James Hurst never completely details Doodle's physical challenges, but it seems likely the boy suffered from a weak heart that prohibited him from attaining the strength and stamina of his older brother. When Doodle is an infant, the family fears he will not live long and even builds him a coffin. The older brother, who is never named, is disappointed in Doodle. He was hoping for a robust playmate that he could run, swim and box with. With great perseverance, he eventually is able to teach Doodle to walk when the boy is five, but fails in his attempts to make his brother as physically able as he is.

While Doodle is physically limited, there is no suggestion that he is mentally challenged. In fact, the opposite seems to be apparent. Doodle is a bright young boy who is particularly interested in nature. He has a vivid imagination and creates detailed fantasy stories involving beautiful peacocks and boys who can fly. These stories are obviously his way of wishing that he was not so physically impaired. His intelligence and sensitivity are on display when the ibis dies in the family's yard and he insists on burying it and singing over the grave. In the end, his body gives out and he is the victim of internal bleeding after chasing his brother through a rainstorm.  

Athough the reader is never told exactly what is wrong with Doodle, the sickly little brother in James Hurst's short story "The Scarlet Ibis," he undoubtedly was suffering from a weak heart, physical disabilities and possibly even mental retardation. William Armstrong is unable to walk until he is forcibly taught by Brother, though he can crawl backwards, reminiscent of a doodlebug--thus the origin of his nickname. His parents originally think that he would not survive and, later, that he may not be "all there," but Brother later determines that, in fact, "he's all there!" This may or may not have been true, since Doodle's speech and learning skills seem to have been somewhat arrested as well.