Type 2 diabetes is a risk factor for Alzheimer’s disease and Parkinson’s disease. Insulin signaling in the brains of people with Alzheimer’s disease or Parkinson’s disease is impaired. Preclinical studies of growth factors showed impressive neuroprotective effects. In animal models of Alzheimer’s disease and Parkinson’s disease, insulin, glia-derived neurotrophic factor, or analogues of the incretin glucagon-like peptide-1 prevented neurodegenerative processes and improved neuronal and synaptic functionality in Alzheimer’s disease and Parkinson’s disease. On the basis of these promising findings, several clinical trials are ongoing with the first encouraging clinical results published. This gives hope for developing effective treatments for Alzheimer’s disease and Parkinson’s disease that are currently unavailable. Type 2 diabetes is a risk factor for Alzheimer’s disease and Parkinson’s disease. Insulin signaling in the brains of people with Alzheimer’s disease or Parkinson’s disease is impaired. Preclinical studies of growth factors showed impressive neuroprotective effects. In animal models of Alzheimer’s disease and Parkinson’s disease, insulin, glia-derived neurotrophic factor, or analogues of the incretin glucagon-like peptide-1 prevented neurodegenerative processes and improved neuronal and synaptic functionality in Alzheimer’s disease and Parkinson’s disease. Several basic trials are ongoing with the This gives hope for developing effective treatments for Alzheimer’s disease and Parkinson’s disease that are currently unavailable.