Regression analysis of field data has indicated that minimum daily temperatures below 11°C delay the development of cotton (Gossypium hirsutum L.) seedlings beyond what would be expected based on the accumulated degree-day sum. In Australian cotton production systems, events where the minimum daily temperature falls below this value are referred to as ‘cold shocks’. The number of cold shocks is used by growers and advisors in assessing retardation of crops in their areas. However, this effect has not been tested explicitly. The aim of this work was to empirically assess effects of cold shock on pre-flower development of cotton plants. Cotton seedlings were grown in controlled-temperature glasshouses. Plants were transferred to cold chambers ranging from 5 to 22°C during the night period for durations from 3 to 10 days. Negative effects were not seen until plants had been exposed to at least 10 nights at 10°C, or for at least 5 nights at 5°C. When differences were generated it did not delay development to first square any more than 4 days, nor was the effect consistent. These differences translated into delays to first flower, but had little effect on plant morphology, or on dry weight measured soon after flowering. In one experiment, a significant reduction in leaf photosynthesis was measured at two times of day on the day after cold shock at 5°C. Improving understanding of the effects of temperature extremes on cotton growth and development will help in developing more functional decision-support tools and field management strategies.