[Vaginal cytology: the importance of the transformation zone and how to obtain an adequate sample].

Cytology smear is the test most frequently used to detect cancer of the uterine cervix. Much is written concerning it in its three phases, analytical, post-analytical, and preanalytical; the later implies sampling and preservation and is the purpose of this review. According to the national literature, result of the sampling is deficient in 64% of cases. Many instruments have been developed to take good samples, and statistically there is no difference between these in terms of achieving the goal of taking a good sample; despite this in Mexico bad samples persist. In this paper it is analyzed the source of these errors that are principally from ignoring the anatomy of the cervix, the handling and fixation of the sample, among others, and some observations are made that are not described in other articles in the same field. Some of the most popular instruments available in Mexico to take samples are the endocervical brush, spatula, and brush (Pappette) here described; their advantages and disadvantages are included, according to the type of cervix in which is going to be used, stressing some details concerning the transformation zone and how to select the best instrument. The results improved with these observations from 45 to 77% in taking good samples.