The aim was to determine if a low serum albumin (SA) level was associated with the occurrence of new onset atrial fibrillation (NOAF) during the first 48 h of intensive care unit (ICU) admission.Overall, 97 patients admitted to the ICU were included in this prospective study. NOAF during the first 48 h was defined as irregularity and absence of p-waves on the continuous electrocardiogram, lasting longer than 2 min. Association were analysed using logistic regression with correction for confounding variables in multivariable analysis.The incidence of NOAF during the first 48 h of ICU admission was 18%. SA levels at ICU admission were significantly associated with NOAF after correction for confounders (odds ratio [OR] 0.86, 95%CI 0.77-0.97, p = .010). SA levels were also significantly associated with the number of episodes of NOAF in multivariate analysis (-0.09 episodes, 95%CI [-0.15/-0.04], p = .001), but not with the presence of sinus rhythm at 48 h (OR 1.05, 95%CI [0.93-1.12], p = .46).In this small hypothesis generating study low levels of SA were associated with the occurrence of NOAF. It remains to be shown if increasing SA levels lowers the incidence of NOAF.