Participant socio-demographic characteristics and referral reason were investigated in relation to completion and health outcomes in a Primary Care Physical Activity Referral Scheme using a prospective population-based longitudinal design. Participants (n = 1735) were recruited over a 2-year period. A three-stage binary logistic regression analysis identified the factors associated with the outcomes of completion (model 1), body mass reduction (model 2) and blood pressure reduction (model 3). Participant's age, gender, ethnicity, occupation and referral reason were the independent variables for model 1, with the variables of completion added in model 2 and completion and body mass reduction added in model 3. Logistic regression analysis revealed that increasing age is associated with the likelihood of completion (Odds Ratio, OR = 1.019; Confidence Interval, CI = 1.008-1.030; P = 0.001). Participants with a pulmonary condition are less likely to complete (OR = 0.546; CI = 0.346-0.860; P < 0.01) compared to those referred for cardiovascular conditions. For ethnicity, in comparison to the white category, patients in the mixed category are significantly more likely to achieve a reduction in body mass (OR = 3.991; CI = 1.191-13.373; P < 0.05). Those who complete are more likely to achieve a reduction in body mass (OR = 3.541; CI = 2.721-4.608; P < 0.001). When compared to the unemployed category, the skilled manual category had an increased likelihood of achieving a reduction in blood pressure (OR = 1.875; CI = 1.044-3.227; P < 0.05). Participants who completed also demonstrated an increased likelihood of a reduction in blood pressure (OR = 1.680; CI = 1.250-2.003; P < 0.001). Furthermore, those participants who achieved a reduction in body mass had an increased likelihood of achieving a reduction in blood pressure (OR = 1.292; CI = 1.008-1.641; P < 0.05). Completion is associated with health outcomes of reduced body mass and blood pressure.