Neuropsychological and psychopathological modifications induced by dopaminergic drugs in patients with Parkinson's disease (PD) are invariably not taken into sufficient consideration by the neurologist. Among the former, modifications of sexual urges and behaviours are of particular importance with regard to severity and variety of clinical pictures. Although rare, such modifications may assume the connotations of an aberrant sexual behaviour with criminal implications, in line with a diagnosis of paraphilia. The authors report the case of a 51-year-old male PD patient who, after a few years of dopaminergic treatment with pergolide, developed a paraphilic disorder, consistent with DSM-IV TR diagnosis of frotteurism, and delusional jealousy. The patient presented mild motor impairment and lack of or negligible cognitive deterioration, thus providing evidence that these disorders are not typical of advanced PD. Pergolide was reduced and quetiapine, an atypical neuroleptic, was introduced with subsequent subsiding of the paraphilic disorder and improvement of delusional jealousy.