We have summarized chemical, physical, and microbiological characteristics of Quaternary Ammonium Salts: particularly, benzalchromium chloride and didecyl-dimethyl-ammonium chloride characteristics were analyzed. These compounds may act as antimicrobial agents in different way: 1) they are surface-active agents and will denature protein or cause dissociation of an enzyme from its prosthetic group; 2) they may alter the cell permeability of bacteria and yeasts; 3) they may stimulate the glycolysis reaction and 4) may inhibit oxidation of lactate. These latest activities may play a role in maintenance of physiologic microbial ecology of vagina or in the re-establishment of the vaginal ecosystem after vaginitis or vaginosis. We have also summarized the physiologic variation of vaginal ecosystem during the different phases of women's life and the microbiology of vagina during vaginitis and vaginosis. The results of more recent studies about the therapeutic role of quaternary ammonium compounds in vulvo-vaginal infections an in vaginosis are synthetically reported. We concluded that quarternary ammonium compounds are efficacious, handy and safe, in obstetrics and gynecology. A very good compliance and low costs of these compounds suggest that they may be used alone as well in association with specific antimicrobial agents in the treatment of most of gynecological infections, and particularly in bacterial vaginosis.