Cumulative data obtained from two relatively large pedigrees of a unique reciprocal chromosomal translocation (RCT) t(1;11)(p36.22;q12.2) ascertained by three miscarriages (pedigree 1) and the birth of newborn with hydrocephalus and myelomeningocele (pedigree 2) were used to estimate recurrence risks for different pregnancy outcomes. Submicroscopic molecular characterization by fluorescent in situ hybridization (FISH) of RCT break points in representative carriers showed similar rearrangements in both families. Meiotic segregation patterns after sperm analysis by three-color FISH of one male carrier showed all possible outcomes resulting from 2:2 and 3:1 segregations. On the basis of empirical survival data, we suggest that only one form of chromosome imbalance resulting in monosomy 1p36.22→pter with trisomy 11q12.2→qter may be observed in progeny at birth. Segregation analysis of these pedigrees was performed by the indirect method of Stengel-Rutkowski and showed that probability rate for malformed child at birth due to an unbalanced karyotype was 3/48 (6.2±3.5%) after ascertainment correction. The risk for stillbirths/early neonatal deaths was -/48 (<1.1%) and for miscarriages was 17/48 (35.4±6.9%). However, the probability rate for children with a normal phenotype at birth was 28/48 (58.3±7.1%). The results obtained from this study may be used to determine the risks for the various pregnancy outcomes for carriers of t(1;11)(p36.22;q12.2) and can be used for genetic counseling of carriers of this rearrangement.