After struggling with gambling and aggression during his service as a soldier, St. Camillus returned to the hospital which dismissed him earlier and became its director. He provided care for the dying and sick, particularly those who struggled with alcoholism. He also attended to the needs of the wounded soldiers of the battle and instituted the Nursing Orders of Ministers.

During his time, St. Camillus was able to establish a hospital for alcoholics. He was also able to develop the first ambulance service. The use of the present sign of the red cross was attributed to St. Camillus de Lellis.

Despite being known for his healing gifts, St. Camillus suffered from the non-healing wound in his leg for most of his lifetime. At 32 years of age, he decided to become a priest only to resign in 1607 to have more time in taking care of the sick.