Officials say 39 Russian soldiers in one unit have been hospitalized and one has died from pneumonia in the Krasnoyarsk Krai region in Siberia.
Lieutenant Colonel Vadim Koval of Russia's Missile Forces said all 40 soldiers are from the Uzhur missile unit.
Koval cited unnamed medical experts as saying that the pneumonia was caused by a virus and "the issue is not connected to hypothermia."
Russian human rights organizations and the Soldiers' Mothers group have previously criticized a Defense Ministry decision in 2010 to introduce new military uniforms, which were designed by prominent Russian fashion designer Vadim Yudashkin.
The critics say the uniforms are not suited for the extreme cold in Siberia, where the temperature is currently about -30 Celsius in some areas.