In this book, Ahmad Abdel Hady discusses the subject of stochastic models, their types, properties, and uses. Follow-up studies are also discussed with particular focus on their design and uses in the medical fields. A case study is explained where stochastic models are used in hepatitis disease in Kalyobia governorate in Egypt. The author proposes a modified model to deal with the case study, which contained more than 400 patients who were followed for approximately 5 years. Results of the application indicated the probabilities of moving along the disease cases, the duration of stay in each case, and the probabilistic number of patients in each case. This book can be of benefit to practitioners in Applied Statistics especially researchers in Medical Statistics.