A cross-sectional study was conducted to determine the prevalence and predictors of adherence to modern antihypertensive pharmacotherapy among slum dwellers in Kolkata, India. Prevalence of adherence based on patient self-reports of consuming =80% of the prescribed medications over a recall period of 1 week was found to be 73% (95% confidence interval = 68%-78%). Compared with their counterparts, the following patients were more likely to be adherent to treatment: patients hypertensive for =5 years (2.98 times), those whose hypertension was detected during checkups for conditions related to hypertension (2.35 times), those living with =4 family members (2.01 times), those with family income of =3000 rupees (2.56 times), those who were getting free drugs (4.16 times), patients perceiving current blood pressure to be under control (2.23 times), and those satisfied with current treatment (3.77). Those adherent to their prescribed medications were 1.71 times more likely to achieve adequate control of hypertension compared with those who were not adherent.