BACKGROUND Placenta is a multifunctional fetomaternal organ that plays an important role during pregnancy. Gestational diabetes mellitus (GDM) is reflected on placenta both macroscopically and microscopically as enlargement of placenta, abnormalities in villi and degenerative changes. METHODS This is a cross sectional study conducted among two groups, normal group and GDM group, to compare the gross features of GDM placentae in the Department of Obstetrics and Gynaecology and Department of Anatomy, Govt. Medical College, Thiruvananthapuram. RESULTS The study was conducted on 65 normal and 65 GDM placentae. There was an increased incidence of gestational diabetes mellitus in the age group > 25 years with a mean age of 26.38 ± 3.84 years. Multiparous women have been found to be more prone to gestational diabetes mellitus. Past history of abortions and intrauterine death (IUD) was more in GDM group as compared to normal group. Incidence of lower segment caesarean section (LSCS) was also more in GDM group. Weight, diameter and number of maternal cotyledons of placentae were significantly increased in GDM. The predominant shape of placenta in both groups was round, next to that was oval. Only 3 placentae showed irregular shape and that was from GDM group. Most common type of attachment of umbilical cord was eccentric in both groups. Next to that was central and marginal respectively. Only one placenta was furcate and that belonged to GDM group. Fetal membrane was translucent in all normal and GDM placentae. Mean birth weight of the baby of GDM mothers was significantly increased. Mean fetoplacental weight ratio was significantly decreased in GDM group as compared to normal group. CONCLUSIONS In the present study, GDM placentae showed significant changes in gross features. Meticulous gross examination of a placenta prior to histologic sectioning enhances microscopic interpretation. By increasing our understanding of the placenta, it may be possible to prevent and treat placental abnormalities related to GDM, thus ensuring lifelong health of the child and the mother. Hence, the present work would provide vital information to both obstetricians and neonatologists. KEY WORDS Placenta, Gestational Diabetes Mellitus, Morphology of Placenta