OBJECTIVES:  Clarify ambiguous and conflicting conclusions of a published Diabetes Prevention Program (DPP) and DPP Outcomes Study (DPPOS) cost-effectiveness study of placebo, metformin, individual and group lifestyle (ILS and GLS) interventions and indicate the degree of uncertainty around them by performing a probabilistic sensitivity analysis (PSA). METHODS:  We took various types of cost (inside and outside DPP) and effectiveness (QALYs) numbers from the original publication and reproduced the original deterministic ICER results. We then explored how the significant ambiguity of the original paper’s conclusions could be clarified by using a net benefit (NB) formulation and the cost-effectiveness plane. We also explored uncertainty through a PSA, assigning probability distributions for costs and outcomes and doing a simulation, producing net benefit results for each set of drawn values and constructing cost-effectiveness acceptability curves and frontiers (CEAC/Fs). RESULTS:  The NB formulation and the cost-effectiveness plane clearly indicated that GLS dominates or is cost-effective relative to the other three interventions for any likely WTP threshold (if that GLS alternative is eliminated, ILS is shown to be the cost-effective alternative, ICER= $17,692). Metformin is only the cost-effective alternative if the WTP is quite low (less than $1665/QALY). The PSA and CEAC/F analyses show that the GLS intervention probability of being cost-effective varies, but GLS is the clear optimal choice throughout (and beyond) a wide range of “reasonable” WTP values ($10,000 – $200,000/QALY). Its conditional probabilities of being cost-effective are P(CE|WTP=$1600) = 0.34); (P(CE|WTP=$100,000) = 0.66). CONCLUSIONS: The original paper's ambiguous/conflicting conclusions (e.g. “policies should support the funding of intensive lifestyle and metformin interventions”) obscure the simplicity of the results. The value of various depictions of deterministic and probabilistic results is shown by clarifying the original results – if these data reflect the performance of the interventions accurately, GLS is the cost-effective alternative in diabetes prevention.