One of the most common and unsatisfying situations encountered in medical genetics clinics is the child with multiple congenital anomalies (MCAs) suggestive of an underlying syndrome for whom it is not possible to make a definitive diagnosis. We undertook a qualitative, descriptive study to learn more about the ways in which the lack of a diagnosis affects parental coping and adjustment to their child's special needs. Semistructured interviews were conducted with 29 parents of 16 children born with an unidentified MCA syndrome. Interviews were based on a small number of open-ended questions, with follow-up probing, asking about parents' experiences with seeking a diagnosis, obtaining treatment and special services, explaining their child's problems to others, reproductive decision making, and support group participation. Transcripts of interviews were analyzed to identify the principal themes surrounding parents' beliefs about the significance of diagnostic information. The parents in this study had been aware of their child's anomalies for 2-23 years, and all had sought multiple evaluations to find a diagnosis. A majority of parents were still interested in identifying their child's syndrome, but most felt that their interest in a diagnosis had diminished over time, and some felt that there were benefits in not having this information. We identified six areas where parents claimed a diagnosis would have impact: labels, causes, prognosis, treatment, acceptance, and social support. Significant issues included obtaining special education services, anticipating the child's future and potential medical complications, life expectancy, recurrence risks, finding sources of social support, and ensuring that the child was receiving appropriate treatment. We conclude that the significance of diagnostic information is complex and varies for different parents. Providers should explore the underlying issues associated with a parental quest for a diagnosis in order to identify and address specific concerns. Published 2001 Wiley-Liss, Inc.