Mycoplasma bovis is an emerging cause of disease in calves. Although it has been around since the 1960's, Mycoplasma associated diseases seem to be showing up more. Once thought to be a relatively rare problem associated only with "large" herds, Mycoplasma now is being identified commonly on farms of all sizes. Although there are several types of Mycoplasma that have been reported in association with disease in cattle, Mycoplasma bovis is by far the most common and is the one routinely associated with disease in calves. This article, which originally appeared in the June 2008 issue of Hoard's Dairyman, explains this strain of Mycoplasma and treatment and control options.