An epidemic of thyrotoxieosis in 1984-1985 was traced to the ingestion of ground beef that was contaminated by bovine thyroid tissue in the tri-state area of Minnesota, South Dakota, and Iowa. This article describes a case of possible thyrotoxicosis-induced violent aggressiveness and firesetting in a 4-year-old boy affected by this epidemic. Although psychosocial factors were initially considered primary, dietary factors eventually proven to be etiologic. This child showed spontaneous decreases in violent behavior during two admissions to a hospital (where thyroid-laced beef was not available) and recurrences with returning home (where he ate contaminated ground beef). A literature review on neuropsychiatrie manifestations of pédiatrie thyrotoxieosis revealed that thyrotoxieosis in children may present with subtle symptoms (new onset of ADHD, drop in school grades) or overt neuropsychiatrie disorders (anxiety, mood, cognitive or psychotic disorders). However, the literature did not appear to have revealed previous reports of violent aggressiveness or firesetting in children. Our case suggests that thyrotoxieosis is able to induce or exacerbate behavioral deterioration, including marked aggressivity, in susceptible children. Clinicians should watch for thyrotoxieosis, which may occur without thyroid disease for a variety of reasons. Delayed treatment can result in enduring physical, cognitive, and emotional disturbances.