Ozanimod is an oral small molecule sphingosine 1-phosphate receptor modulator approved for relapsing forms of multiple sclerosis (RMS) and moderately to severely active ulcerative colitis (UC) and under development for Crohn’s disease. Ozanimod and its major active metabolites CC112273 and CC1084037 block lymphocyte egress from lymphoid tissues, reducing the absolute lymphocyte count (ALC) in blood. To characterise the influence of patient characteristics on ALC response, a population pharmacokinetic/pharmacodynamic (PK/PD) analysis was conducted.