The internet has the potential to foster healthy lifestyles and to support chronic disease management. Older adults could benefit from using the internet and other information and communication technology to access health-related information and interventions available online. The aim of this study was to investigate factors influencing internet use in older and oldest age groups and to determine the frequency of internet use for health-related purposes. Using data from a nationally representative telephone survey of older adults aged 75 years and over, a sample of 999 people was assessed using structured clinical interviews. Descriptive and binary logistic regression analyses were performed. Overall, 42.6% (418/999) of participants used the internet. Among those, 55.7% (233/417) searched the internet for health-related information. Regression analyses revealed that internet use was significantly associated with younger age (odds ratio OR 0.89, 95% CI 0.85-0.92; P<.001), male gender (OR 2.84, 95% CI 2.02-4.00; P<.001), higher education levels (OR 6.69, 95% CI 4.48-9.99; P<.001), a wider social network (OR 1.04, 95% CI 1.01-1.07; P=.01), higher health-related quality of life (OR 1.02, 95% CI 1.00-1.03; P=.006), lower levels of depressive symptoms (OR 0.89, 95% CI 0.80-0.99; P=.04), and higher rates of chronic illness (OR 1.12, 95% CI 1.04-1.21; P<.004). This study provides population-representative data on internet use in old age in Germany. People in the older and oldest age groups participate in online activities. Understanding the factors that are associated with older adults internet use can contribute to developing tailored interventions and eHealth (electronic health) services to improve well-being in older adults.