Introduction: Hypertensive disorders in pregnancy are an important cause of maternal mortality in Sri Lanka. Gestational hypertension (GH)/Pre-eclampsia (PEC) and threatened miscarriage (TM) share common pathophysiological mechanisms. This study was conducted to determine the association between TM and development of GH/PEC. Methodology:A case control study was conducted at Castle Street Hospital for Women, Sri Lanka from May 2014 to May 2015. Cases consisted of patients with GH/PEC and compared with age and parity matched controls. A systematic random sampling method was used. Similar number of cases and controls were compared while each group consisted of 245 subjects. Data was obtained from medical records. Patients aged 20-35 years were included and medical disorders other than GH/PEC were excluded.Results: There were 245 subjects in each group of the study. Among the cases, 56% had GH and the rest had PEC. There were 25 patients had a history of TM in the study population. About 6.5% of cases had a history TM, while only 3.6% of controls had TM. There is also a significant risk of developing PEC in a patient who had a history of threatened miscarriage (OR 3.31,. Moreover the patients who had a history of TM tend to develop GH or PEC early, within 20-32 weeks of gestation (OR 11.49,). As we identified, 62% of patients who had TM developed GH/PEC early (from 20 to 32 weeks) but among the cases who had no history of TM, only 12% developed GH/PEC between 20 to 32 weeks of gestation (O.R. 20.7 (5.66 to 91.96). There is a significant risk of developing severe GH/PEC in the group of patients who had a history of TM (OR 8.59,. Eighty one percent (81%) of the cases, who had a history of TM, developed severe and moderate GH/PEC rather than mild. But the majority (63%) of the cases, who had no history of TM, developed mild GH/PEC (O.R. 7.6 (2.00 to 42.55).Conclusions: Shared pathophysiological mechanisms of GH/PEC and TM may explain the observed association between these obstetric complications. Early onset, severe GH/PEC in cases with TM suggests temporality and a biological gradient which favors causality.