Physicians, Dickens scholars, and historians have tried to diagnose the condition that affected Tiny Tim in A Christmas Carol. Leading entities include tuberculosis (TB), rickets, malnutrition, cerebral palsy, spinal dysraphism, and renal tubular acidosis. This article posits that an examination of the environment of London of 1820 to 1843 (when the novella was written) can provide important clues as to his condition. The blackened skies from burning coal, the crowding of people in tenements, the limited diet of the underclass, and the filth of London resulted in a haven for infectious diseases and rickets in children. Sixty percent of children in London had rickets, and nearly 50% had signs of TB. Tiny Tim likely had a combination of both diseases. After Ebenezer Scrooge's transformation, Scrooge could have ensured an improved diet, sunshine exposure, and possibly cod liver oil for Tiny Tim, which could have led to a "cure." Dickens was familiar with both rickets and TB and wrote about cod liver oil as a possible cure for rickets and scrofula. Improved vitamin D status can result in enhanced macrophage synthesis of 1,25-dihydroxyvitamin D, which increases the synthesis of the antimicrobial peptide cathelicidin (LL-37). This component of the innate immune system has strong killing properties for Mycobacterium tuberculosis. The combination of rickets and TB represent a crippling condition that could be reversed by improved vitamin D status.