Introduction: The death of a relative after an intensive care unit stay can lead to mental disorders as post-traumatic stress disorder or complicated grief. During the first SARS-CoV-2 lockdown in France, social restrictions limited the opportunity to apply family-centered care in intensive care unit, increasing the risk of post-traumatic stress disorder or complicated grief.Methods The psychiatric and other intensive care unit teams at Toulouse University Hospital, France, have created a temporary service known as OLAF (Opération de Liaison et d’Aide aux Familles). OLAF provided psychological phone support to family members of intensive care unit patients. Then, we investigated the impact of the OLAF service on complicated grief, comparing the prevalence of 12-month complicated grief after death in two groups: relatives provided with support via the OLAF service and a control group (standard of care).Results Of the twenty-five bereaved family members recruited, five (20%) presented with complicated grief at twelve months. The groups had no difference on complicated grief diagnosis. An explanatory model found that complicated grief symptoms intensity was mainly explained by post traumatic disorder symptoms intensity (R2 = 0.73, p = 6.21e− 05*). As the only factor significantly associated with complicated grief intensity, we found a predictive value of post-traumatic stress disorder score on complicated grief diagnosis at twelve months in a ROC curve model.Conclusion There was no difference in the prevalence of complicated grief with OLAF service. Failing to prove its effectiveness, we found post-traumatic stress disorder symptoms intensity on the PTSD Checklist for DSM-5 (PCL-5) as the only factor associated to complicated grief in our cohort. We found that this scale could also predict the complicated grief risk at twelve months.Trial registration: The study was approved by our ethics board (CPP 2020-54, ClinicalTrials.gov, Identifier: NCT04470869), and all participants provided informed oral consent.