BACKGROUND--Vascular access for cardiac catheterisation of children and young adults who have had previous catheter procedures is often difficult. OBJECTIVE--To assess the influence of age at and type and technique of previous cardiac catheterisation on the ease of vascular access for subsequent study of paediatric and adolescent patients. SETTING--Tertiary referral centre for paediatric cardiology. PATIENTS--478 Consecutive patients aged 1 day to 19 years undergoing cardiac catheterisation over a 12 month period, including 131 patients who had had previous catheterisation(s). METHODS--Prospective study, recording for each patient the age, weight, diagnosis, vascular access (artery, vein, or both), vessels eventually catheterised, access time, total duration of the procedure, and details of any previous catheter studies. RESULTS--Of 131 patients who had had previous catheterisations, 80 (61%) had been studied once previously, 38 (29%) twice, and 13 (10%) on three or more occasions. The right femoral vessels were cannulated without difficulty in 72 cases (55%). Elective cannulation of left femoral vessels (because of scar tissue on the right side) or upper body vessels was undertaken in 18 cases (14%). Problems cannulating the right femoral vessels were encountered in 41 cases (31%); the vein was blocked in 29, the artery in six and the femoral veins were blocked bilaterally in six cases. The mean (SD) access time was significantly prolonged in these 41 children (41(18) v 21(13) minutes, p < 0.001) as was total duration of the procedure (116(31) v 94(34) minutes, p < 0.001). Children who had had a saphenous vein cut down as neonates subsequently had a blocked ipsilateral femoral vein in 10/15 cases (67%). Risk factors for problematic cannulation also included a higher number of previous catheterisation procedures. CONCLUSIONS--Difficulties with vascular access are common in children and adolescents who have had previous cardiac catheterisations. In those who have had cut down or multiple previous studies, elective entry to the left femoral vessels should be undertaken and procedure time may be prolonged. Such cases should therefore be performed under general anaesthesia.