Abstract: The novel viral agent, TT Virus (TTV), is a non-enveloped, single-stranded and circular virus, DNA virus that was originally identified in the serum of patients with non-A to E post-transfusion hepatitis. TTV transmission can occur by the parenteral route, but faecal-oral transmission may also occur. The aim of this study was to detect the occurrence of TT virus DNA in children with collagen vascular diseases who received multiple transfusions of blood or one of its products and to determine the risk factors for infection with TT virus. The study included 80 children with collagen vascular diseases who received repeated transfusions of blood or its products: 20 patients with dermatomyositis (DM), 20 patients with Juvenile Rheumatoid Arthritis (JRA) and 40 patients with Systemic Lupus Erythematosus (SLE), aged 8-18 years. Serum samples were analyzed for TTV-DNA, HCV and HBsAg. Samples were also analyzed for biochemical liver profiles. TTV-DNA is positive in 35% of Egyptian children suffering from autoimmune diseases who received multiple transfusions of blood or blood products. The positivity of TTV-DNA in DM, JRA and SLE were 30, 50 and 30%, respectively. The highest coinfection with TTV and HBsAg was 66.7% in SLE followed by 20% of JRA. Multiple infections of TTV, HBsAg and HCV were 16.7% in SLE. HEV was negative in all studied groups.