Some physicians recognize the mild form of Metal Fume Fever (MFF); few recognize MFF's serious form. Mild MFF is self-limited and is caused by inhaling metal oxide fumes. Serious MFF may be life-threatening and is caused by inhalation of military smoke. Initial manifestations of the two forms are similar but their pathophysiologies and managements are different. Mild MFF patients recover within 48 hours and rarely require hospitalization. Serious MFF symptoms remit but may relapse 24 to 48 hours later with significant morbidity and mortality. Serious MFF patients require admission for observation. Military physicians need to differentiate these forms of MFF.