Mild cognitive impairment (MCI) is present in on average one-fourth of Parkinson’s disease (PD) patients with no dementia diagnosis. Only recently has PD-MCI been treated as a new diagnostic entity. In 2012, unified criteria were adopted which allow both diagnosing MCI in Parkinson’s disease (PD-MCI) and further classification taking into account the profile of cognitive dysfunctions and the probability of evolution towards dementia. The diagnostic criteria were presented in the form of stipulations and guidelines assuming that diagnostic process is based on the neuropsychological assessment of the patient. The notion of MCI had been borrowed and for a couple of years had been relying on definitions developed in relation to Alzheimer’s disease. For the first time, in the proposed criteria memory dysfunction is not the basis of classification. Only two categories of dysfunctions have been retained, single-domain and multiple-domain. Whether the adopted criteria will contribute to an accurate diagnosis of cognitive dysfunctions and PD-specific dementing processes remains an open question. In spite of some limitations, the presented criteria can certainly improve the efficacy of monitoring the patient’s state at the same time allowing the hope for an appropriate therapy and a higher quality of life. Moreover, the unification of diagnostic criteria will be crucial in assessing usefulness of neuropsychological test instruments as a basic method of investigating neurodegenerative processes not only in PD.