Pigmentary demarcation lines are abrupt transition lines that separate areas of hyperpigmentation from areas of normal skin. They were first described by Matsumoto in 1913 (Navea et al. in Cureus 9, 2023). Their etiology and pathogenesis are unknown, but their distribution appears to follow Voigt lines (Zieleniewski et al. in J Cosmet Dermatol 18:700–702, 2019) and could correspond to differences in melanocyte spread, probably influenced by genetic and hormonal factors. There are eight subtypes of pigmentary demarcation lines but the most common ones are type B lines associated with pregnancy. They are mostly found in patients with high Fitzpatrick skin types, and they affect the lower extremities. Diagnosis is by clinical and the lines typically appear during the second/third trimester and disappear postpartum.We report a case of 31-year-old resident doctor from Uttar Pradesh (India) in the 32 week of a low-risk first pregnancy. She presented with asymptomatic diffuse areas of hyperpigmentation that had appeared progressively on the posterior aspects of her thighs and legs to form symmetric lines on the medial portion of both extremities. The lines form a distinct boundary between the hyperpigmented and normal skin. Also there is presence of the linea alba and acanthosis nigricans. The findings led to a diagnosis of type B pigmentary demarcation lines associated with pigmentary changes in pregnancy.