As stated in the first part of this review, growth hormone (GH) acts on all organs and tissues, and untreated GH-deficient (GHD) patients suffer from several affectations occurring as a consequence of the lack of this key hormone. In the second part of this review, we will analyze the effects of GH on the liver, the kidney, the adrenal glands, the skeletal muscles, the bones, the hematopoietic system, the gastrointestinal system, and the adverse effects that may occur in these organs and systems in the GH deficiency not treated in children and adults. Apart from these, we conclude that GH is a co-hormone that seems to be necessary for the physiological actions of other important hormones in humans.