The objective of the study was to evaluate the sociodemographic characteristics and to find out the causes of infertility among the couple attending out patient department of infertility unit in Bangabandhu Sheikh Mujib Medical University (BSMMU) from January to December 2007. This is a descriptive observational study. Data were analyzed done manually and statistical analysis was calculated by Statistical package for social sciences (SPSS) program. During this period 3184 patients were attended out patient department (OPD) of infertility unit (IU-I & II). Among them primary infertility was present in 1971(61.90%) and secondary infertility in 1213(38%) cases. One thousand four hundred and two (1402) patient's complete data were reviewed from OPD register book of IU-I. The mean duration of the infertility was 4.7(4.52) years. The mean age of female patient was 26.5±5.35 years. The mean age of male patient was 34.56±6.33 years. A positive male factor problem alone was found in 13% couples, female factors in 71.46% couples and unexplained infertility in 15.47% couples. Among the male factor Oligozoospermia (33.33%) was the most common cause of male infertility. Anovulation (52.16%) was the most common cause of female infertility and major cause of anovulation was Polycystic ovary syndrome (PCOS) (29.90%). Fibroid uterus, Bilateral tubal block and Pelvic inflammatory disease (PID) were significantly (p<0.001) higher in secondary infertility. Endometriosis and unexplained infertility were significantly (p<0.001) higher in primary infertility. Distribution of other causes of infertility was same for both primary and secondary infertility.