In the episode Look Back to Yesterday, Albert Ingalls is studying to be a doctor at university. While studying, he begins to feel ill and Doc Baker intervenes after Albert collapses, insisting he sees a doctor at the hospital to discover what is causing his nosebleeds and his collapse.
Albert is eventually diagnosed with leukemia, a type of cancer.
The ending of the episode does raise questions about whether Albert was terminally ill or not. The ending of this episode implies that Albert passes away from leukemia, but in another episode narration by Laura, she reveals he returns to Walnut Grove 20 years later to work as a doctor. There is still speculation today about whether Albert dies or not.