Unconditional cash transfers (UCTs; provided without obligation) for reducing poverty and vulnerabilities (e.g. orphanhood, old age, or HIV infection) are a social protection intervention addressing a key social determinant of health (income) in low‐ and middle‐income countries (LMICs). The relative effectiveness of UCTs compared with conditional cash transfers (CCTs; provided only if recipients follow prescribed behaviours, e.g. use a health service or attend school) is unknown. To assess the effects of UCTs on health services use and health outcomes in children and adults in LMICs. Secondary objectives are to assess the effects of UCTs on social determinants of health and healthcare expenditure, and to compare the effects of UCTs versus CCTs. Two review authors independently screened potentially relevant records for inclusion, extracted data and assessed the risk of bias. We obtained missing data from study authors if feasible. For C‐RCTs, we generally calculated risk ratios for dichotomous outcomes from crude frequency measures in approximately correct analyses. Meta‐analyses applied the inverse variance or Mantel‐Haenszel method using a random‐effects model. Where meta‐analysis was impossible, we synthesised results using vote counting based on effect direction. We assessed the certainty of the evidence using GRADE. This body of evidence suggests that unconditional cash transfers (UCTs) may not impact a summary measure of health service use in children and adults in LMICs. However, UCTs probably or may improve some health outcomes (i.e. the likelihood of having had any illness, the likelihood of having been food secure, and the level of dietary diversity), two social determinants of health (i.e. the likelihoods of attending school and being extremely poor), and healthcare expenditure. The evidence on the relative effectiveness of UCTs and CCTs remains very uncertain.