The BCG is administered to all the newborns at birth in Iran. Systemic adverse reactions to BCG vaccine such as osteomyelitis and disseminated BCG infection are rare. This is a retrospective study of 15 cases <72 months who were admitted with systemic syndrome compatible with disseminated mycobacterial disease during 2004–07. Disseminated BCG disease occurred in eight children younger than 6-months old and 12 patient younger than 12-months old. Twelve patients were male. Nine of 15 patients had well known primary immune deficiency disorders including severe combined immunodeficiency, chronic granulomatous disease; cell mediated immune defect and HIV infection. Nine (60%) cases had good response to four anti-mycobacterial drug therapy and interferon gamma. Disseminated BCG disease is a rare but devastating complication of BCG vaccination that should be considered in the appropriate clinical setting. Severe immune-compromised infants are at greatest risk and they respond poorly to standard therapies.