Due to its proven clinical effectiveness, lithium has been considered as a corner stone for the long-term treatment of Bipolar Disorder (BPD) for more than half a century. The objective of this study was to evaluate the effect of patients' different co-variables on lithium pharmacokinetics and the development of a pharmacokinetic model for the estimation of lithium clearance in Egyptian bipolar patients; this model can be used afterwards during dosage adjustment to achieve target's steady-state plasma concentrations in similar settings. The study was conducted on 65 adult Egyptian bipolar patients of both genders, in both the in-and outpatient settings in the