Background Following single-twin death, the perinatal mortality and morbidity for the surviving co-twin is increased but difficult to quantify. We present data on prognosis from a systematic review.Objectives We aimed to determine the incidence of a) co-twin death, b) neurological abnormality and c) preterm delivery for the surviving co-twin following single-twin death after 14 weeks of gestation.Search strategy Literature was identified by searching two bibliographical databases and specialist journals between 1990 and 2005.Selection criteria The selected studies of ‡5 cases reported on perinatal death and/or neurodevelopmental delay of the surviving co-twin.Data collection and analysis Studies were assessed for quality and data extracted to allow computation of rates. The data were inspected for heterogeneity using a Forrest plot and examined statistically using the chi-square test. Data from individual studies were pooled within subgroups defined by prognosis.Main results The search strategy yielded 632 potentially relevant citations. Full manuscripts were retrieved for 54 citations and 28 studies were finally included in the review. Following the death of one twin, the risk of monochorionic and dichorionic co-twin demise was 12% (95% CI 7-11) and 4% (95% CI 2-7), respectively. The risk of neurological abnormality in the surviving monochorionic and dichorionic co-twin was 18% (95% CI 11-26) and 1% (95% CI 0-7), respectively. The risk of preterm delivery was 68% (95% CI 56-78) and 57% (95% CI 34-77), respectively. Where there was comparative data within studies, the odds of monochorionic co-twin intrauterine death was six times that of dichorionic twins .87]). Neurological abnormality was also higher in monochorionic compared with dichorionic pregnancies ]).Author's conclusions More prospective research is required to inform decision making on this subject, especially with data that allow stratification based upon chorionicity.