OBJECTIVES: . To establish the correlation of log mean cost with respect to APACHE II score, pre-hospitalization and length of hospital stay. To determine the intragroup variance of log mean treatment costs in different parameters. METHODS: Categorical data was presented as frequencies with percentages and was analyzed by Chi-square test, log regression and Pearson correlation. A logarithmic transformation was used for total cost to convert into normal distribution. Geometric mean and Geometric SD was used to summarize total cost. One way ANOVA was used to compare the mean of log (total cost) across various categorical variables. Multiple linear regression was used to find the factors associated with total cost of hospitalization of OPP. Correlations was used for measuring the strength of linear relationship between total cost and APACHE II score.  RESULTS: A significant variance in log mean treatment costs was observed in different parameters like pseudocholinesterase levels, type of poison consumed, anticholinergics administered and incidence of intermediate syndrome. A high mean cost was observed in patients with a pseudocholinesterase level of less than 2000 and those who consumed WHO class Ib pesticide.  A cost difference of INR 25,000 was noted in patients who developed intermediate syndrome. The APACHE II Score, pre-hospitalization period and length of hospital stay had significant correlation with log cost. Among the variables, length of hospitalization had strong correlation with log cost (r=0.673, p<0.001). For every one-unit increase in pre-hospitalization period, APACHE II score and length of hospital stay, the log cost increases by INR 1.01, 1.27 and 1.5 respectively CONCLUSIONS: High costs of treatment coupled with a proportionately great loss of man-days, make OPP an extremely important area for pharmacoeconomic evaluation and for framing appropriate policies for remedial measures. Hence studies evaluating treatment regimens with respect to costs and outcome are highly desirable.