Introduction: Neonatal jaundice is a common clinical problem observed during the first week of life affecting approximately 60% of term and 80% of preterm infants. While majority of these infants recover, in a proportion of infants, jaundice may become severe, progressing to acute bilirubin encephalopathy (ABE) or kernicterus with a substantial risk of neonatal mortality. Phototherapy for neonatal jaundice is a common treatment in neonatal medicine and is used to prevent the neurotoxic effects of bilirubin. There is evidence that its use is associated with hypocalcaemia which is a serious concern. However, the frequency of hypocalcemia varies greatly between the studies ranging from as low as 6% to as high as 80%. The type of fluorescent tube, serum vitamin D, bilirubin levels and also the patient’s skin colour might be responsible for this variation in the existing literature. Owing to the observed variation among various populations and lack of local such local published material, need for the present study was felt. Objective: The objective of this study was to determine the frequency of hypocalcaemia after 48 hours of phototherapy in full term infants presenting with neonatal jaundice at a teaching hospital in Punjab. Material and Methods: It was a descriptive case series. This study was conducted at Department of Pediatric Medicine Unit-I, Lahore General Hospital, Lahore. And the duration of this study was 6 months after the approval of synopsis from 27 January 2016 to 26 July 2016. This study involved 246 full term neonates of both genders presenting with neonatal jaundice with serum calcium level >8 mg/dl before the start of phototherapy. These patients were followed for the development of hypocalcemia (serum calcium ≤8 mg/dl). A written informed consent was taken from parents of each patient. Results: The mean age of the patients was 6.04±3.50 days. There were 149 (60.6%) male and 97 (39.4%) female patients with a male to female ratio of 1.5:1. The weight of the neonates ranged from 2 kg to 3 kg with a mean of 2.64±0.23 kg. 162 (65.9%) neonates have weight more than 2.5 Kg. Serum calcium level upon admission ranged from 8.1 mg/dl to 12.0 mg/dl with a mean of 9.04±0.93 mg/dl. Majority (69.1%) of the neonates had serum calcium at admission between 8.1-9 mg/dl followed by 76 (30.9%) neonates whose serum calcium at admission was ≥9 mg/dl. Mean serum calcium level after 48 hours of phototherapy was 7.69±0.54 mg/dl with a mean decrease of 1.35±0.90 mg/dl. This difference was statistically significant (p=0.000). 167 (67.9%) neonates had hypocalcemia. There was no significant difference in the frequency of hypocalcemia across age (p=0.964), gender (p=0.812), weight (p=0.994) and serum calcium level at admission (p=0.904). Conclusion: The frequency of hypocalcemia was found to be 67.9% in full term infants with neonatal jaundice undergoing phototherapy. There was no significant difference in the frequency of hypocalcemia across age (p=0.964), gender (p=0.812), weight (p=0.994) and serum calcium level at admission (p=0.904). KEYWORDS: Neonatal Jaundice, Phototherapy, Hypocalcemia