In this paper, a simulation model of the glucoseinsulin system for a patient undergoing diabetes Type 1 is developed by using a causal modeling approach under system dynamics. The OpenModelica simulation environment has been
employed to build the so called causal model, while the glucoseinsulin model parameters were adjusted to fit recorded mean data of a diabetic patient database. Model results under different
conditions of a three-meal glucose and exogenous insulin ingestion patterns have been obtained. This simulation model can be useful to evaluate glucose-insulin performance in several circumstances, including insulin infusion algorithms in open-loop and decision support systems in closed-loop.