Abstract Objective: The aim of the study was to compare obstetric results in two groups of pregnant women (patients that had and had not planned their pregnancy) suffering from pregestational diabetes mellitus (PGDM). Material and methods: 400 women with PGDM were divided into two subgroups: planned pregnancy (P) (N=200) and unplanned pregnancy (NP) (N=200). The study was based on retrospective analysis of data collected at the Department of Obstetrics and Women Diseases, University of Medical Sciences, Poznan, from patients who delivered between 1995-2006. In both groups obstetrical complications and selected neonatal parameters were analyzed. Results: Statistically important differences in obstetric results between the two analyzed subgroups of patients were observed. P-group was metabolically better controlled, both upon admission to our department and in the third trimester. The mean daily insulin requirement among P-group patients was smaller than among pregnant NP-women upon admission to our department. P-patients suffered from miscarriages and stillbirths less frequently. Neonates born to P-mothers had higher gestational age at delivery and their Apgar score and cord blood results were significantly better. Conclusions: Our results confirmed that patients with PGDM who plan their pregnancies achieve significantly better obstetric results compared with unplanned pregnancy group. Pregnancy planning should become a standard of obstetric and diabetic care in this group of patients.