This paper proposes a customer churn model for a private bank in Turkey. It is more challenging to put forth a model for banking sector as there are no contractual agreements between a customer and a bank regarding the duration of services. During the development of the model, we first converted the raw data into a usable and meaningful form. Later, using data mining techniques on our data, we have developed a “churn prediction model”. Prediction performance is evaluated using accuracy, sensitivity, specificity, kappa statistic and area under the curve based measures.