Complex atrioventricular septal defect (complexAVSD) with outflow obstructions, heterotaxia, unbalanced ventricular volumes and systemic and pulmonary venous abnormalities remains a challenge with complex staged surgical procedures.  Objective: To study long-term survival in complexAVSD, in a national Swedish cohort.   Methods: National birth-, malformation- and death registers were searched for the AVSD diagnosis. A retrospective study of hospital charts and databases for the AVSD diagnosis was made at all centers for pediatric cardiology and heart surgery in Sweden. ComplexAVSD was defined as any combination of AVSD (with a common atrioventricular valve) with outflow obstructions to the pulmonary or systemic circulations or unbalanced ventricular volumes.  Age at death, age at surgery, type of palliative or corrective procedure and other cardiac and extracardiac malformations were also recorded. All infants born alive with complexAVSD from 1973 to 1997 (25 years) were included and recorded as dead or alive on May 28, 2008.Results: 237 infants with complexAVSD were born alive 1973-1997 in Sweden.  Down syndrome was diagnosed in 84 (35%) and heterotaxia  in 71 (30%).  Surgery was performed in 139/237 (59%) and age at first operation decreased significantly from 4,9 ±4,0 to 0,5±0,8 years during the study period (p<0,01).  17 were palliated with TCPC. Corrective surgery was completed in 69 of 139 operated.  Only 56/237 subjects were alive at end of study with a median follow-up time of  16,6 (10,4-35,2) years.  Total mortality decreased from 85% to 67% (p<0.01)Conclusion:  Mortality has been significantly reduced in complexAVSD but long-term survival is still poor at only 33%.