critical illness cover is benefit policy and it helps an insured when he comes across approx. 10 diseases like cancer, renal failure, strokes, multiple sclerosis etc. the insured has to survive 30 days after such diseases are known. the benefit of these policies may be availed once only. normally, this cover is given to professionals who have mediclaim insurance with the same company. normally this policy has some waiting period also say 90 days. i hope, now, its clear to you. please let us know in case you have any query.