There is a growing concern among health authorities that an increasing number of people in the Western world become overweight and even obese. It is well known that obesity is related to several diseases (e.g., diabetes, stroke, and high blood pressure) and that such diseases related to obesity lead to early death. It has also been discussed whether overweight and obesity in themselves or in relation to such diseases lead to cognitive decline. On the basis of data from a large, population-based, prospective study we examined three cognitive domains: episodic memory, semantic memory, and spatial ability. Two body measures were used to define normal weight and overweight, body-mass index and waist/hip ratio. Although these two body measures reveal quite different prevalence data of overweight, the associations between overweight and cognition are similar. For episodic memory, overweight interacts with age, but when controlling for hypertension, stroke and diabetes, this interaction disappears. For semantic memory, normal weight participants outperform overweight participants even after controlling for these diseases. For spatial ability, the well-established advantage for men holds for young-old and old-old normal-weight participants. For overweight participants, this advantage holds for middle-age participants only. We conclude that there is a weight-cognition relationship even after controlling for obesity-related diseases. The results are discussed in terms of possible biological mechanisms.