Hypertension is one of the chronic diseases with the highest incidence worldwide and a cause of considerable mortality and disability. This paper aims to evaluate the effect of mobile phone text messaging on adherence to hypertension treatment. A quasi-experimental before-after intervention was conducted based on interviews with patients from a chronic disease outpatient program. Four groups were formed, one of which was the control group. The groups intervened were sent encouraging educational text messages at varying frequencies for a period of two months. At the close of the intervention, participants were asked to fill in the Martín Bayarre Grau questionnaire to determine their adherence to antihypertensive treatment before and after the intervention. A bivariate analysis was performed comparing the variable adherence to treatment before and after the intervention in the four study groups. A significant difference was only found in Group 3 (p = 0.011). This group was sent eight messages per month (two messages per week). Additionally, a comparison between the intervention groups and the control group conducted at two months found a significant difference in Group 3 (p = 0.022). The intervention proved was useful to improve adherence in the study population. A positive response was obtained in Group 3, who received eight messages per month.