Trisomy 13 syndrome is a lethal chromosomal disorder characterized by severe congenital anomalies. We report a case of trisomy 13 syndrome with semilobar holoprosencephaly, cyclopia, proboscis, omphalocele, and an absent nasal bone, prenatally diagnosed by first‑trimester ultrasonography. The diagnosis was confirmed by chromosomal analysis. The pregnancy was eventually terminated at 14 weeks of gestation. The poor prognosis of trisomy 13 syndrome and holoprosencephaly prompts the demand for early prenatal diagnosis. We present this case to introduce some of the typical features of semilobar holoprosencephaly, including an anteriorly fused ventricle with partially fused thalami and absent falx, and to sensitize physicians to similar sonographic findings in the future.