In pathological brain, a variety of morphological forms exist that reflect differences infunctional requirements. To better understand microglia function in neurological disease, it is important to identify and quantify microglia morphology associated with specific neuropathologies. Traditional feature parameters such as area or cell diameter are not sufficient. In this study microglia were quantified by the box-counting fractal dimension (DB). 104 cells from post mortem tissue were analysed comprising cells of controls, Alzheimer's disease, schizophrenia and affective disorder. The DB was significantly different from control (1.36) compared to schizophrenia (1.41),Alzheimer's disease (1.41) and affective disorder (1.43) with p < 0.01. Thus fractal analysis provides a useful quantitative and objective measure of microglial form associated with normal function and diverse neuropathology. The distribution of fractal dimensions associated with microglia structure and activation with disease progression also differs, suggesting a different aetiology for these diseases.