The nutritional status of a patient determines to a great extent his/her susceptibility and capacity in responding to infections. Protein and caloric malnutrition as well as many selective mineral and vitamin deficiencies deteriorate the immune and inflammatory metabolic response, increasing the frequency of infections and worsening their evolution and prognosis. Furthermore, recurrent infections can deteriorate nutritional status, with both problems forming a vicious circle that needs to be recognized for adequate treatment. This problem is not as foreign to us as we might think, given that many hospitalized patients as well as those with chronic diseases suffer from serious nutritional deficiencies. If we also take into account the proposition that the nutritional status of a patient can affect his/her response to treatment with antibiotics and vaccines, we realize then that not enough attention has been paid to this important public health risk factor to date.