Solid waste collection and disposal is a growing problem for all major cities in Turkey. Istanbul, as the biggest city containing a great number of industries, has a large amount of wastes to dispose of. Currently, two recently constructed landfill sites for the storage of solid wastes are in operation: one on the European side (Odayeri, Kemerburgaz) and the other on the Asian side (Komurcuoda, Sile), both of which are old mining pits. The findings of the studies conducted for the site selection and design of these landfill sites within the framework of the Turkish Environmental Impact Evaluation Regulation, are presented. The investigations have included the assessment of geological, geomorphological, hydrogeological and geotechnical characteristics of the sites. They have indicated that these sites are suitable for storage with no adverse environmental effects until the projected operation year of 2020. The sites have been operating since March, 1995. There were some geotechnical problems faced during the construction and operation phases. The results and recommendations for remedial measures based on back-analysis are also given.