To describe the clinical and radiological features, diagnosis, and treatment of an epidemic outbreak of tuberculosis in a daycare centre in Zaragoza. The index case was a teaching assistant with a late diagnosis of bacilliferous tuberculosis. Mantoux testing was carried out in all children. In those with a positive Mantoux test, a chest X-ray was performed. Children with an abnormal chest X-ray underwent microbiological investigations. Among all the children in the daycare center, the Mantoux test was positive in 11 children. Chest X-ray was abnormal in 10 children. Of these, seven (70 %) were symptomatic. Chest X-ray showed dense opacification in nine children (90 %) and mediastinal lymph adenopathy in five (50 %). Three children (30 %) had lobar atelectasis requiring bronchoscopy and subsequent steroid therapy. Bacilloscopy was positive in only one child. Gastric juice culture was positive in seven children and the amplified Mycobacterium tuberculosis direct test was positive in a further seven. All microbiological investigations were negative in only one child. Establishing a definitive diagnosis of tuberculosis in children remains difficult and frequently relies on a constellation of clinical findings, radiology and epidemiology in children with a positive Mantoux test. The amplified Mycobacterium tuberculosis direct test has high sensitivity and provides fast results. Epidemic outbreaks continue to be frequent in Spain. Study of contacts shows high efficiency in controlling outbreaks.