"Considering the relation between the speech of "development" and the "seduction it exerts" (Rist, 1996) and the people with mobility difficulty (people depending on wheelchairs or crutches, suffering from temporary or permanent deficiency diseases, old people, pregnant women, obese people, people of low stature and so forth), concepts of accessibility, environment and sustainability are analysed in this essay, topics that have taken a place of highlight and concern in this era of globalization. With the aim of proposing a reflection on the new approaches for the space planning in our cities, the present article starts from the idea the environment matter cannot be dissociated from the social matter. The relation between environment and sustainable development presupposes the integration of economical development and social development. In this context, the article focuses People with Mobility Difficulty (PMD), generally excluded from the spaces in the cities; exclusion that evolves itself by the lack of accessibility to certain resources, among what the urban space itself is the most important one."