A method is presented that can be used to calculate diffraction line profiles from specimens with dislocations numerically. Results for some special dislocation distributions have been compared to the results of an analytical model proposed by Wilkens. Within the bounds of the Wilkens model, good agreement has been found. Moreover, it follows from the calculations that the functional form due to Wilkens describes diffraction lines also very well outside the bounds of the model. Therefore, the model has been extended in a phenomenological way. These findings can be of use for the interpretation of experimental data. As an example, a diffraction line from an Al layer has been investigated. The diffraction line profile was described accurately with the functional form due to Wilkens. However, the results also revealed shortcomings of the model distribution with respect to the true dislocation distribution. This can lead to difficulties in the interpretation of experimental results.