Immediate family members of veterans diagnosed with Gulf War Illnesses (GWI) often complain of fatiguing illnesses, and upon analysis they report similar signs and symptoms as their veteran family members. Since a relatively common finding in Gulf War illness patients is a bacterial infection due to Mycoplasma spp., we examined military families (149 patients: 42 veterans, 40 spouses, 32 other relatives and 35 children with at least one family complaint of illness) selected from a group of 110 veterans with Gulf War illness who tested positive (∼41%) for at least one of four Mycoplasma spp.: M. fermentans, M. hominis, M. pneumoniae or M. genitalium. Consistent with previous results, over 80% of Gulf War illness patients who were positive for blood mycoplasma infections had only one Mycoplasma spp. (Odds ratio = 9.0, 95%CL 3.3–24.3, P >.0.001), in particular M. fermentans (Odds ratio = 17.9, 95%CL 4.1–78.1, P >.0.001). In healthy control subjects the incidence of mycoplasma infection was ∼8.5% and none were found to have multiple mycoplasma species (Multiple species Odds ratio >25, Chi2 = 8.1, P >.0.004). In 107 family members of mycoplasma-positive Gulf War illness patients there were 57 patients (53%) that had essentially the same signs and symptoms as the veterans and were diagnosed with Chronic Fatigue Syndrome (CFS) and/or Fibromyalgia Syndrome. Most of these CFS patients also had mycoplasma infections compared to the few non-symptomatic family members (Odds ratio = 16.9, 95%CL 6.0–47.6, P >.0.001), and the most common species found was M. fermentans (Odds ratio = 40.3, 95%CL 8.7–186.4, P >.0.001). In contrast, in the few non-symptomatic family members that tested mycoplasma-positive, the Mycoplasma spp. were often different from the species found in the Gulf War illness patients. The results suggest that a subset of Gulf War illness patients have mycoplasma infections, possibly obtained as contaminants from multiple vaccines given during deployment, and these infections can be transmitted to immediate family members who subsequently display similar signs and symptoms and are diagnosed with CFS and/or Fibromyalgia Syndrome.