Non-surgical periodontal therapy, including patient motivation, instruction in oral hygiene and thorough scaling and root planing has been shown to be an acceptable and effective treatment for chronic destructive periodontitis. Even in deep periodontal pockets clinical attachment levels may be maintained by scaling and root planing alone provided that effective plaque control is assured by recall appointments at regular intervals. Even if personal oral hygiene procedures do not reach the required standard of perfection, non-surgical periodontal therapy may significantly delay the loss of periodontal attachment. Scaling and root planing are best performed with hand instruments. Ultrasonic devices save some time but leave rough root surfaces which are highly susceptible to the accumulation of further subgingival plaque. The intervals at which scaling and root planing have to be performed in order to alter successfully the pathogenic subgingival flora and to maintain a flora consistent with periodontal health have not been conclusively established. The limitations of non-surgical periodontal therapy lie within the operator's skill at gaining access to all root surfaces in furcations and deep periodontal pockets. Non-surgical periodontal therapy may have to extend over long time periods. For this reason, limited flap surgery in order to gain access to root surfaces, which would otherwise be too time-consuming to treat with scaling and root planing alone, might still be valuable.