Abstract Background To support longitudinal research into mood in adolescents we sought to assess the feasibility of collecting mood data via Short Message Service (SMS) over 3 years, and to investigate the relationship between SMS data and self-report measures of depression. Methods Prospective cohort study of young people aged 9 to 14 years at baseline. Participants completed Short Mood and Feelings Questionnaire (SMFQ) and the Youth Self Report Anxious/Depressed ((YSR)/AD) and Withdrawn/Depressed (YSR/WD) scales at baseline and annually for 3 years. In addition, at 3 monthly intervals they responded to an SMS asking them to rate their mood from 0 to 9 (9 highest). Results 277 young people (43% female) completed all four waves of the survey. There was a 87% response rate to requests for SMS Mood ratings. Mean SMS Mood decreased over time for females (p = 0.006) but not males (p = 0.45). We found an inverse association between SMS Mood and the SMFQ, YSR/AD and YSR/WD, scales in females and the SMFQ and YSR/WD scales in males. 45% of participants reported at least one SMS Mood rating score below 5, while 5% reported clusters of low SMS scores. Clusters of low SMS Mood scores were associated with SMFQ scores in the clinical range at 24 (OR = 4.45) and 36 months (OR = 4.72), and YSR/WD in the clinical range at 36 months (OR = 4.61). Conclusions SMS Mood ratings represent a feasible means to augment but not replace assessment of mood obtained using standard instruments.