From 23 April to 13 May 1995, an outbreak of acute respiratory disease (ARD) hospitalizations occurred in basic training soldiers at Fort Jackson, South Carolina. Weekly hospitalization rates for the most affected military unit reached 11.6%. Virus isolation and serologic studies from a sample of patients identified the agent as adenovirus type 4. Prior to starting vaccinations against adenovirus types 4 and 7 in 1971, these serotypes were the major causes of ARD in basic trainees. No outbreaks were reported when the vaccines were used. A logistical error temporarily interrupted vaccine production, and newly arriving trainees received no adenovirus vaccines from the summer of 1994 through late March 1995. This outbreak occurred in unvaccinated soldiers. The sole manufacturer has permanently stopped adenovirus vaccine production. All type 4 vaccine supplies are now depleted. This outbreak demonstrates continued susceptibility of military recruits to adenovirus type 4 and warns of future outbreaks.