Organophosphorus (OP) is an easily accessible pesticide which has a high morbidity and mortality on human exposure. Serum cholinesterase (SChE) is usually used for assessing the severity of poisoning, in this study we assess the role of serum creatine phosphokinase (CPK) as an alternative prognostic marker. This was a single centred, hospital-based, prospective and observational study, conducted on 88 patients with a history of OP compound consumption who were admitted to the ICU of tertiary care hospital, from the time period October 2019 to March 2021.  The patients were clinically categorized into mild, moderate and severe categories according to Peradeniya Organophosphorus Poisoning (POP) scale and before initiation of treatment, the samples were sent for estimation of SChE and serum CPK.  Out of the 88 patients, OP poisoning was more common in the age group of 21-30 years and males had a higher incidence. Chlorpyriphos (62.5%) was the most common compound. A higher POP score, marked reduction in SChE levels, and increased serum CPK levels were observed to have increased the duration of hospital stay, increased the severity of poisoning, increased the need for ventilator support and also increased the mortality.