Abstract Background Cancer outcomes are poor in socioeconomically deprived communities, with low symptom awareness contributing to prolonged help-seeking and advanced disease. Targeted cancer awareness interventions require evaluation. Methods This is a randomised controlled trial involving adults aged 40+ years recruited in community and healthcare settings in deprived areas of South Yorkshire and South-East Wales. Intervention: personalised behavioural advice facilitated by a trained lay advisor. Control: usual care. Follow-up at two weeks and six months post-randomisation. Primary outcome: total cancer symptom recognition score two weeks post-randomisation. Results Two hundred and thirty-four participants were randomised. The difference in total symptom recognition at two weeks [adjusted mean difference (AMD) 0.6, 95% CI: −0.03, 1.17, p = 0.06] was not statistically significant. Intervention participants reported increased symptom recognition (AMD 0.8, 95% CI: 0.18, 1.37, p = 0.01) and earlier intended presentation (AMD −2.0, 95% CI: −3.02, −0.91, p < 0.001) at six months. “Lesser known” symptom recognition was higher in the intervention arm (2 weeks AMD 0.5, 95% CI: 0.03, 0.97 and six months AMD 0.7, 95% CI: 0.16, 1.17). Implementation cost per participant was £91.34, with no significant between-group differences in healthcare resource use post-intervention. Conclusions Improved symptom recognition and earlier anticipated presentation occurred at longer-term follow-up. The ABACus Health Check is a viable low-cost intervention to increase cancer awareness in socioeconomically deprived communities. Clinical trial registration ISRCTN16872545.