The aim of the study was to explore heterogeneity of change in state affect following the introduction of insulin therapy in patients with type 2 diabetes. State affect was assessed twice among 305 patients: just before the introduction of insulin therapy and at 1-month follow-up. Latent class growth modeling showed that negative affect (NA) increased in 78% of the sample, whereas positive affect (PA) improved in only 17% of the participants. On the basis of cross-tabulation of these changes a 4-class model of emotional response to the new treatment was obtained. The largest subgroup of participants (57%) manifested “threat response”, i.e. moderate-stable PA with increase in NA. Participants in the “challenge response” subgroup (11.8%) showed increases in both NA and PA. The third class (10.2%) characterized by “no response”, had low-stable NA and moderate-stable PA. The smallest “stress response” subgroup (9.8%) showed increase in NA and high-stable PA. Gender, age and education level were significant covariates of group membership. Thus, the findings revealed heterogeneous emotional response to the new treatment, which may be of clinical relevance for improving diabetic patients’ adjustment through a more individual, person-centered approach.