Microtia is thought to have a multifactorial inheritance, but several investigators disagree. Here we report our survey of the hereditary factors and possible causes. We conducted a questionnaire survey of 428 patients with microtia who were being treated at two hospitals from September 2006 to September 2008. We recorded their age, sex, affected side, duration of gestation, birth weight, age of parents at patients' birth, accompanying malformations, number of siblings, familial occurrence, smoking habit of parents, and medication/disorders of mother during pregnancy, and analysed the results. There were preponderances of male (61%), unilateral (90%) and right-sided disease (59%). Other than the first and second branchial arch syndrome, microtia is often accompanied by other congenital deformities, in particular congenital heart disease; cleft lip, or palate, or both; vertebral defects; and anomalies of extremities. The occurrence in first-degree relatives was 2%. Most maternal disorders and medication taken during pregnancy were common and there was no clear link. Statistically, there was a tendency to low birth weight and high maternal age, but it is not possible to identify these as a specific cause of microtia. Multifactorial inheritance is unlikely to be the cause of microtia as there was only one finding in agreement with its widely accepted characteristics. However, we cannot completely discount it as there were too few cases in some groups to make a judgement.